Prosthetic, orthotic or exoskeleton device

ABSTRACT

A time-dependent decay behavior is incorporated into one or more joint actuator control parameters during operation of a lower-extremity, prosthetic, orthotic or exoskeleton device. These parameters may include joint equilibrium, joint impedance (e.g., stiffness, damping) and/or joint torque components (e.g., gain, exponent). The decay behavior may be exponential, linear, piecewise, or may conform to any other suitable function. Embodiments presented herein are used in a control system that emulates biological muscle-tendon reflex response providing for a natural walking experience. Further, joint impedance may depend on an angular rate of the joint. Such a relationship between angular rate and joint impedance may assist a wearer in carrying out certain activities, such as standing up and ascending a ladder.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/740,876, filed on Jan. 13, 2020, which is a continuation of U.S.application Ser. No. 14/407,656, filed Dec. 12, 2014, now U.S. Pat. No.10,531,965, which is a U.S. National Stage Entry of PCT/US2013/045356,filed Jun. 12, 2013, which claims the benefit of U.S. ProvisionalApplication No. 61/658,568, filed Jun. 12, 2012, U.S. ProvisionalApplication No. 61/662,104, filed Jun. 20, 2012, and U.S. ProvisionalApplication No. 61/679,194, filed Aug. 3, 2012. The entire contents ofeach of the above-identified applications is incorporated herein byreference in its entirety.

BACKGROUND 1. Field of the Invention

Devices and control systems for biologically-inspired artificial limbsare generally disclosed.

2. Related Art

Existing prosthetic leg devices include a series-elastic actuator whichfunctions as a biologically-inspired muscle-tendon unit to modulate,during a gait cycle, joint impedance, joint equilibrium and torque, inaccordance with walking speed and terrain modality (e.g., slopingground, stairs, etc.). It is desired for prosthetic leg devices tofunction in a way that matches the human ankle response as captured, inpart, by FIG. 1 , which illustrates human biomechanical function in agait cycle, on level-ground. In the schematic of FIG. 1 , the gait cycleon level-ground is initiated by a heel-strike event. Other types of gaitcycles, such as toe-strike initiated cycles as might occur in steep rampor stair ascent, are not expressly shown.

Prosthetic leg devices have been designed so as to exhibit responsebehavior captured by a “dashboard” of biomechanical characteristics,shown in FIG. 2 a . These biomechanical characteristics are based onbody-mass normalized and walking-speed reference measures from an intactankle population, including Net Non-Conservative Work, Peak Power,Toe-off Angle and Peak Power Timing. As depicted in FIG. 2 a , dashedlines denote +/− sigma error bounds for the normative data, solid linesdenote average values for the normative data, and circles representindividual step data wirelessly acquired from an ankle device wearer.

The ankle device depicted in FIG. 2 b employs a state machine,implemented in the intrinsic control firmware of the device to modulatethe actuator response. The actuator response is programmed to define ajoint impedance, joint equilibrium and torque, so as to emulate humanfunction in each gait cycle state. Depending on the phase of gait, thedevice will enter into an appropriate state. At times, the transition(s)between states for an artificial leg device may be abrupt, or might notaccommodate for changes in wearer intent.

SUMMARY

The inventors have recognized and appreciated there to be advantages inemploying time-dependent decay behavior in one or more controlparameters when the actuator torque of an artificial leg device ismodulated during use. While not meant to be limiting, such parametersmay include joint equilibrium, joint impedance (e.g., stiffness,damping) and/or joint torque components (e.g., gain, exponent) of theprogrammable state (e.g., powered reflex response). The decay behaviormay conform to any suitable mathematical relationship, such as anexponential decay, linear drop, quadratic function, piecewise relation,dynamic behavior model that might arise from the output of a linear ornon-linear differential equation, or other suitable function. Suchbehavior, when used in a positive force feedback system, may provide fora smooth experience that emulates biological kinetics (torque, power)and kinematics. For example, this type of control may case thetransition(s) between states of the device (e.g., so that they aregenerally unnoticeable to the wearer) and may allow for the wearer toalter his/her course during gait in a natural manner.

In an illustrative embodiment, a prosthesis, orthosis or exoskeletonapparatus is provided. The apparatus includes a proximal member; adistal member; a joint connecting the proximal and distal members, thejoint adapted to permit flexion and extension between the proximal anddistal members; a motorized actuator configured to apply at least one ofa joint impedance and a joint torque, the joint impedance including atleast one of a stiffness and damping, wherein the stiffness isreferenced to a joint equilibrium; a sensor configured to detect atleast one of a phase and a change in a phase of joint motion in arepetitive cycle; and a controller configured to modulate at least oneof the joint equilibrium, the joint impedance and the joint torque, themodulation employing a decaying time response as a function of at leastone of the phase and the detected change in phase of joint motion.

In another illustrative embodiment, a method of controlling a jointimpedance and a joint equilibrium of a prosthesis, orthosis orexoskeleton apparatus is provided. The method includes actuating a jointof the apparatus; tracking a current joint position of the apparatus;and controlling a value of the joint equilibrium of the apparatus so asto converge to a value of the current joint position.

In yet another illustrative embodiment, a prosthesis, orthosis orexoskeleton device is provided. The device includes a joint constructedand arranged to permit flexion and extension between a proximal memberand a distal member; a motorized actuator configured to apply at leastone of a joint impedance and a joint torque, the joint impedancereferenced to a joint equilibrium; a sensor configured to detect acharacteristic of the device; and a controller configured to modulate atleast one of the joint equilibrium, the joint impedance and the jointtorque according to the detected characteristic, the modulationexhibiting time-dependent decay behavior.

In a further illustrative embodiment, a prosthesis, orthosis orexoskeleton device is provided. The device includes a joint constructedand arranged to permit flexion and extension between a proximal memberand a distal member: a motorized actuator configured to apply at leastone of a joint impedance and a joint torque, the joint impedancereferenced to a joint equilibrium; a sensor configured to detect anangular rate of at least one of the proximal member, the distal memberand a joint connecting the proximal and distal members; and a controllerconfigured to modulate a parameter comprising at least one of the jointequilibrium, the joint impedance and the joint torque according to thedetected angular rate to include at least one of a rate dependentstiffness response and a decaying response.

In yet another illustrative embodiment, a prosthesis, orthosis orexoskeleton apparatus is provided. The apparatus includes a proximalmember; a distal member; a joint connecting the proximal and distalmembers, the joint adapted to permit flexion and extension between theproximal and distal members; a motorized actuator configured to applytorque at the joint; a sensor configured to detect at least one of aphase and a change in a phase of joint motion in a repetitive cycle; abattery to store electrical energy and to power the apparatus, acontroller configured to short the leads of the motor where thecontroller recovers electrical energy from the apparatus during at leastpart of the repetitive cycle.

Other advantages and novel features of the invention will becomeapparent from the following detailed description of various non-limitingembodiments when considered in conjunction with the accompanying figuresand claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are described with reference to thefollowing drawings in which numerals reference like elements, andwherein:

FIG. 1 illustrates a schematic of a human biomechanical gait cycle onlevel-ground;

FIG. 2 a depicts graphs of walking speed-referenced measures compared tonormative measures from an intact ankle population;

FIG. 2 b shows a perspective view of an artificial ankle device:

FIG. 3 illustrates a schematic of an artificial ankle device:

FIG. 4 shows a state transition graph of two gait cycles of anartificial leg device in accordance with some embodiments;

FIG. 5 depicts a state transition graph of a heel-strike-first lateswing to an early stance transition in accordance with some embodiments;

FIG. 6 illustrates a state transition graph of a toe-strike-first lateswing to an early stance transition in accordance with some embodiments;

FIG. 7 shows a state transition graph of a heel-strike initiated earlystance to a late stance transition in accordance with some embodiments;

FIG. 8 depicts a state transition graph of a late stance to a latestance power transition in accordance with some embodiments:

FIG. 9 shows a state transition graph of a late stance power to an earlyswing toe-off detection in accordance with some embodiments;

FIG. 10 a illustrates a graph of data correlating torque rate with pitchrate in accordance with some embodiments;

FIG. 10 b depicts a graph of data correlating pitch rate with walkingspeed in accordance with some embodiments;

FIG. 10 c shows a graph of the correlation data between torque rate andpitch rate in accordance with some embodiments;

FIG. 11 depicts a schematic diagram of operation of an artificial legdevice in accordance with some embodiments:

FIG. 12 illustrates an artificial leg device system architecture inaccordance with some embodiments;

FIG. 13 shows a schematic of a knee state machine with state transitionsin accordance with some embodiments;

FIG. 14 depicts a graph of knee kinematics for a typical gait cycle;

FIG. 15 shows graphs of early stance exponential stiffness and dampingresponses in accordance with some embodiments:

FIG. 16 a illustrates a graph of rate-dependent early stance springstiffness in accordance with some embodiments:

FIG. 16 b shows a schematic of a wearer in a sitting position inaccordance with some embodiments:

FIG. 16 c shows a schematic of the wearer of FIG. 16 b in a sittingposition in accordance with some embodiments:

FIG. 16 d shows a schematic of the wearer of FIGS. 16 b-16 c in anupright position in accordance with some embodiments;

FIG. 17 a shows a graph of a piece-wise constant and linear dampingconstant as a function of knee flexion in accordance with someembodiments:

FIG. 17 b shows a graph of a piece-wise linear and quadratic dampingconstant as a function of knee flexion in accordance with someembodiments;

FIG. 17 c shows a graph of an angular rate as a function of extensionangle in accordance with some embodiments:

FIG. 18 depicts a graph of a ground reaction force used to detect a footstrike transition in accordance with some embodiments:

FIG. 19 illustrates the frequency response of a self-adjusting jointequilibrium impedance:

FIG. 20 shows normative ankle angle, angular velocity, moment, and powerdata plotted as a percentage of the gait cycle;

FIG. 21 depicts a relationship between net non-conservative ankle workand walking speed of walkers with intact limbs on level-ground;

FIG. 22 shows normative ankle angle-torque and velocity-torque plots forthe stance phase of a single gait cycle:

FIG. 23 depicts ankle torque versus ankle angle plotted for eachsubphase of a gait stance; and

FIGS. 24-25 illustrate graphs of reflex parameter modulation functionsin accordance with some embodiments.

DETAILED DESCRIPTION

Various embodiments of the present disclosure relate to abiologically-inspired, sensing and control architecture for bionic legactuation (e.g., knee joint actuation, ankle joint actuation). Asdescribed herein, a bionic device may function to restore or replaceanatomical structure(s) and/or exhibit physiological process(es), withone or more electro-mechanical components. For instance, bionic devicesof the present disclosure may emulate stance-phase kinetics (e.g.,torque and power) that may occur naturally in intact limbs. Bionic legjoints described herein may employ a series-elastic actuator (SEA) toamplify mechanical power, to enable closed-loop torque control and toenable sensing of actuator torque through a model of thetorque-displacement characteristics. In some embodiments, an ankledevice may employ a hardstop with known flexion characteristics thatlimits dorsiflexion travel of the joint. A control system modulatesjoint impedance (e.g., stiffness, damping), joint equilibrium (e.g.,equilibrium location) and joint torque (e.g., motor reflex gain, motorreflex exponent) in accordance with gait cycle state and walking speed,a surrogate for walking speed, or the rate of change of a state variableor sensor in the actuator control system. In some embodiments, the rateof change of the state variable may include an inertial pitch rate(e.g., of a tibial component) and/or an actuator torque rate (e.g., ofan ankle or knee joint), shortly after foot strike.

In some embodiments, one or more parameters controlled by the system mayexhibit time-dependent behavior. For example, the joint impedance, jointstiffness, joint damping, joint equilibrium, reflex torque gain, reflextorque exponent, or another suitable parameter(s) may employ a timedecay (e.g., value of the parameter diminishes over time) during anappropriate phase of gait. Such a decay may exhibit any suitablefunctional behavior, such as exponential, linear, piecewise, etc. Thistype of behavior, in some cases, may also provide for a naturalexperience to the wearer, for example, without producing a feeling ofabruptness upon changes in the phase of gait. For instance, a graduallessening of ankle stiffness upon entry into an Early Stance mode mayallow for a wearer to rollover smoothly in a natural manner such thatmode changes (i.e., state transitions) of the device are transparent(e.g., almost unnoticeable).

As used herein, a phase of gait may describe a particular state of thedevice, which may be triggered by a gait event (e.g., heel-strike,toe-off). For example, a phase of gait may refer to: a state transitionin a leg prosthesis control system, such as in a joint actuatorcontroller; the inertial state of proximal and distal members of thedevice; and/or changes in one or more components of the inertial stateof the proximal and distal members of the device.

As used herein, a motorized actuator or motorized actuation system mayinclude any suitable motor. For example, motorized actuators mayincorporate one or more electric motors, hydraulic motors, pneumaticmotors, piezo-actuated motors, shape-memory motors, electro-polymermotors, or any other appropriate motorized device.

As used herein, a characteristic of motion of a device may include oneor more of the following: an inertial pose of distal and proximalmembers of the device; changes in the inertial pose of the distal andproximal members of the device; translational velocity or angular rateof one or more points on the distal and proximal members; kinetics,including force, torque and power, and the derivatives thereof at thejoints and at the interface between the device and ground; kinematics,including joint angles, and derivatives thereof; dynamic actuatorstate(s), including force, torque, displacement in the motor drive andtransmission, including the elastic elements embodied within thetransmission; and other appropriate characteristics.

While neuroscientists identify increasingly complex neural circuits thatcontrol animal and human gait, biomechanists have found that locomotionrequires little outside control if principles of legged mechanics areheeded that shape and exploit the dynamics of legged systems.Embodiments according to the present disclosure may include musclereflex response(s) that encode principles of legged mechanics, andprovide a link to the above observations surrounding the behavior ofnatural limbs. Equipped with reflex control, various embodiments ofbionic devices presented herein reproduce human walking dynamics and legkinetics and kinematics; tolerate ground disturbances; and adapt toslopes without outside parameter intervention(s), such as mightotherwise be informed by inertial sensor inputs, neural or cognitivefunctions. Accordingly, aspects/parameters of the bionic response may beappropriately encoded to adaptively modulate one or more parametersbased upon intrinsic kinematic and kinetic measures (e.g., angle andtorque including their derivatives) or extrinsic interventions arisingfrom measures of walking speed and terrain (as might be supplied by aninertial measurement unit, for instance), so as to suitably emulate themuscle-tendon reflex. Aspects described herein may employ principlesdescribed in the article by Geyer, H. and Herr, H, entitled “AMuscle-Reflex Model that Encodes Principles of Legged Mechanics ProducesHuman Walking Dynamics and Muscle Activities,” submitted to IEEETransactions on Neural Systems and Rehabilitation Engineering andaccepted in 2010, the disclosure of which is hereby incorporated hereinby reference in its entirety.

It can be appreciated that embodiments of the present disclosure are notrequired to incorporate a state machine that transitions from onediscrete state to another in a gait cycle. For instance, a mere changein inertial state across a gait cycle (e.g., based on the use of a rategyroscope to measure a rate of tibial pitch) may be a pail of a gaitcycle phase.

Systems described herein may be incorporated in devices made by iWalk.Inc., such as in the BiOM^(T2). In some cases, the BiOM^(T2) deviceemploys a series-elastic actuator (SEA) that incorporates abiophysically-based, reflexive control system. This system emulatesdominant muscle-tendon behavior, during walking, of the ankle plantarflexors, the Soleus and Gastrocnemius calf muscles, as well as thedominant dorsiflexor, the Tibialis Anterior. The SEA may control anklejoint impedance (e.g., stiffness, damping), virtual spring equilibriumand/or reflexive torque. The SEA system may enable sensing of actuatortorque (Γ_(SEA)) through measurements of series-spring deformation.Additionally, the ankle joint may include a hardstop, which limits theability for the ankle to move to a position of increased dorsiflexion,after a certain point. In addition to measuring actuator torque, thesystem may also monitor hardstop torque (Γ_(hs)), through themeasurement of hardstop spring deformation.

A finite state machine may be employed in a State Control Processor tocontrol transitions of the device through different states. The gaitcycle states in the State Machine may include early stance, late stance,late stance power, early swing and late swing, which are aligned withthe conventional names employed in human biomechanics, namely,controlled plantar flexion, controlled dorsiflexion, powered plantarflexion, early swing and late swing, respectively. The transitionsbetween these walking gait phases may be determined by a system clock(time) and/or the SEA torque (Γ_(SEA)), hardstop torque (Γ_(hs)), andtheir time derivatives.

In some embodiments, the device includes a single finite state machinefor walking. As a result, when a single finite state machine isemployed, the control system does not revert to a non-walking statemachine based on biomechanical change(s) made by the human wearer.Accordingly, the device is less cumbersome than would otherwise be thecase if multiple state machines are incorporated.

The system may make some or all motor control actuation decisions basedupon kinetic sensory information of the device (e.g., force/torqueinformation), without requiring kinematic sensory information of thedevice (e.g., positions, velocities, accelerations). For example, thesystem is not required to employ reflex response parameter interventionsas these might be informed by accelerometers or rate gyros or any othersensor for the measurement of overall device positions, velocities oraccelerations relative to horizontal or vertical reference planes toadapt to walking speed and terrain modality. As a result, the positionof the ankle joint may be controlled based on the interaction forcesexperienced between the human wearer, the device, and the groundsurface. Therefore, contrary to conventional robotic systems, it is notnecessary for the device to directly control the position of the anklejoint, whether in stance or swing phases, as systems described hereinare controlled based on reflex response(s). Though, it can beappreciated that, in some cases, the system may employ position sensors,accelerometers, rate gyros and/or any other sensor, as suitably desired.

Non-linear, positive force feedback control is applied in poweredplantar flexion to emulate human muscle-tendon reflex dynamics. Devicesdescribed herein employ positive force feedback with intent to emulate anatural, uncontrolled (e.g., automatic) reflex response. This reflex isimplemented by a motor torque control that behaves according to apositive force feedback mathematical relationship involving parametersthat include torque gain and torque exponent, each modulated accordingto the stimulation of certain parameters, for example, the torque ratemeasured by a series elastic actuator and/or the torque measured at ahardstop.

The system control architecture employs motor and joint angle sensing tocompute, via calibrated models, instantaneous SEA and hardstop torque.Instead of using inertial information, the system architecture employsintrinsic measures of torque, torque rate of change and time durationwithin a gait cycle state to inform transitions in the State Machinethat directs the response modulation in a Motor Processor and, in someembodiments, may rely exclusively on torque and time within a state toinform the transitions. That is, measurements of inertial information,such as position, velocity and acceleration are not used to informparameter interventions that modulate the actuator response. Rather,force measurements, such as force and torque measured over time, may beused as input to direct the response modulation of the joint actuator.

The device may exhibit reflexive behavior, without any system memory.That is, the system may monitor device torque(s) and reflexively respondto such torques) with little delay between sensing and actuation. As aresult, the monitoring of torque throughout or during a portion of agait cycle may be the basis for modulation of control actions during acurrent gait cycle, without any consequence to control actions thataffect a subsequent gait cycle.

In some embodiments, the control system does not require detection ofparticular gait patterns or events, and in response, the control systemis not required to modulate either the control algorithm, or its systemparameters. The control algorithm and its parameters are not necessarilyadjusted in any manner in response to a user transitioning from a walkto a run, nor while ambulating from a level-ground surface to anincline, nor from level-ground to steps, nor while moving to standing,nor from a standing position to a sitting position, nor from a standingposition to a leaning position, nor from a sitting position to a lyingdown position, nor while putting on pants. That is, despite the type ofaction the wearer may currently be performing, the control system mayfunction according to a single state machine control, without regard tothe type of user action currently performed.

The control system may be configured to detect a foot strike with theground surface based on torque/force information. Independently of howthe device has struck the ground, whether it is a heel strike, a toestrike, or a foot-flat strike, the system may run the same algorithmwith the same control parameters.

Further, walking speed may be estimated from a known linearly correlatedrelationship with normalized, peak derivative of SEA torque in latestance. That is, torque rate may be used as an estimate (or surrogate)of a current walking speed so as to inform the reflex parametermodulation. In particular, the gain and exponent parameters of a reflexrelationship may be modulated based on a rate of change of a parameter(e.g., pitch rate, torque rate). For example, a rate-based blending(interpolation) of the parameters may be employed.

In addition, to achieve a smooth and natural response, in someembodiments, the stiffness and/or damping of the joint in Early Stancemay be designed to decay exponentially, for example, smoothly reducingstiffness/damping so as to increase joint compliance. Such exponentialdecay behavior, for impedance, may be particularly beneficial for awearer of an artificial leg device when walking slowly on uneven terrainor descending down a steep slope, allowing for seamless, hi-fidelitydevice control.

In some embodiments, artificial leg devices are constructed according toa biologically-inspired approach where an IMU is not required for theiruse. A number of design principles are considered in constructing theartificial leg device.

For example, the time duration in a state, torque and torque derivative(torque rate) may guide the device in transitioning from one state toanother, as well as to modulate the reflex parameters, which may or maynot correlate with a current walking speed. In some cases, a singlemeasured parameter may be sufficient as a signal for transitioning thedevice between states and/or estimate walking speed. As discussed, timeduration within a state. SEA torque (Γ_(SEA)) and hardstop torque(Γ_(hs))—and the time derivatives of these—may be used as parametersthat the system uses to inform state transitions and, in some cases, maybe used independently and/or exclusively from other parameters. Peak SEAtorque rate as sampled during late stance may be employed in theadjustment of the late stance power reflex, which may occurindependently of an estimation (or correlation) of walking speed. Assuch, it may be a useful observation, yet not necessary for embodimentsof the present disclosure, that the above-mentioned rate(s) maycorrelate with walking speed, for a broad range of wearers. As such, itis not necessary in the preferred embodiment to explicitly estimate thewalking speed and to use that estimate to inform the reflex responsemodulation. So, the intrinsic inertial, kinematic or kinetic may be useddirectly to inform that modulation.

As muscle-tendon units of an intact limb do not employ inertial sensingto modulate their response, such intrinsic measures may enable thedevice to behave and respond as a more natural muscle-tendon unit.Instead, in an intact ankle, muscle and tendon stretch (torque) andtheir various rates of change are key inputs to the spinal reflex arcconnecting the tendon and the muscle. As a result, transitions are morenatural and consistent even when the wearer walks softly or runs andjumps in place.

Further, the system may employ a uniformly-applied stiffness/impedancethat decays smoothly after foot strike. When the impedance after footstrike is set to decay, “impedance switching” between states, and theabrupt nature that often accompanies such a switch, may be eliminated.Early Stance impedance—generally defined by stiffness (k_(es)) anddamping (b_(es))—may be used by all states, except, in some cases, itmight not be used during late stance power and early swing. Impedancemay be set in late-swing to a programmable (tuned) value. In someembodiments, k_(es) decays exponentially to a programmable value, k

, which is typically a small fraction of the initial value, k_(es) _(0′).

Exponential decay of impedance, or one or more other appropriateparameters, may begin at entry into Early Stance. In some cases, thetime constant for decay may be set so that the stiffness issubstantially maintained (e.g., does not drop quickly) during controlledplantar flexion (CP) (e.g., a time duration between 0.05-0.2 seconds),such as when walking at a brisk walking speed. When walking more slowly.e.g., down a steep hill, the stiffness may be set to drop smoothly, ormore quickly, so as to enable the foot to find an equilibrium state atfoot-flat with a diminished spring restoring torque—thereby reducingsocket stress. The exponential decay behavior (e.g., for jointimpedance, joint equilibrium, torque, or others) may continue for aportion of or for the entire gait cycle. For instance, in some cases,exponential decay may continue until it is reset at entry into EarlyStance. Such transitions may occur without the wearer even noticing theoccurrence of a state transition—thereby eliminating confusion andirritation.

A single walking state machine may deliver a biomimetic response eitherwhile walking or not walking, without need for a secondary non-walkingstate machine. Instead of discretely switching between a non-walkingstate machine and a walking state machine, state machines of the presentdisclosure may use the Early Stance state to uniformly deliver abiomimetic response without having to reconfigure the joint impedanceand/or joint equilibrium when in a non-walking state. To accomplishthis, the walking state machine may cause transition(s) to Early Stanceif the time duration within any of the other walking machine statesexceeds a programmable limit for that state, typically about twoseconds. The stiffness, k_(es) may continue to decay to deliver asmoothly varying impedance that, in the limit, devolves to asubstantially lightly damped response that responds naturally fornon-directed activities that do not involve locomotion. As discussedabove, for some embodiments, only torque and torque derivatives are usedto inform the logic transition between states, for example, from earlystance to late stance and late stance power where locomotion may then beinitiated.

In some embodiments, spring impedance (e.g., stiffness, damping) may bedependent on angular rate in, for example, an ankle or a knee. Forinstance, an artificial joint device may employ a bionic control systemthat modulates the impedance of the joint so as to assist the wearerduring stair ascent, steep ramp ascent or during the transition fromsitting to standing. In some cases, when flexed past a certain thresholdangle, the spring stiffness of the joint may be rate dependent, applyingpositive feedback in response to increases in the joint angular rate orthe absolute value of joint angular rate. As an example, the springstiffness of an artificial knee joint may be modulated such that when awearer is standing up and the angular rate is increased, the jointbecomes stiffer so as to provide increased support during the standingmotion. Such support is effective to assist the wearer in standing up.

The present disclosure relates to U.S. Pat. No. 8,075,633 entitled“Active Ankle Foot Orthosis”; U.S. patent application Ser. No.13/349,216, entitled “Controlling Powered Human Augmentation Devices”;U.S. patent applications entitled “Hybrid Terrain AdaptiveLower-Extremity Systems” corresponding to Ser. Nos. 61/231,754;12/552,013; 12/552,021; 12/552,028; 12/552,036; and 12/551,845; U.S.patent application entitled “Biomimetic Transfemoral Prosthesis”corresponding to Ser. No. 61/554,921; U.S. patent application entitled“Powered Ankle Device” corresponding to Ser. No. 61/595,453; U.S. patentapplication entitled “Under-Actuated Exoskeleton” corresponding to Ser.No. 61/659,723; U.S. patent application entitled “Walking State Machinefor Control of a Bionic Ankle Joint” corresponding to Ser. No.61/658,568; U.S. patent application entitled “Bionic Control System foran Artificial Ankle Joint” corresponding to Ser. No. 61/662,104; U.S.patent application entitled “Biomimetic Ankle and Knee Actuator Designs”corresponding to Ser. No. 61/451,887; U.S. patent application entitled“Terrain Adaptive Powered Joint Orthosis” corresponding to Ser. No.13/417,949; U.S. patent application entitled “Powered Joint Orthosis”corresponding to Ser. No. 13/347,443; U.S. patent application entitled“Using Knee Trajectory as a Discriminator in a Prosthesis or Orthosis”corresponding to Ser. No. 61/435,045; U.S. patent application entitled“Terrain Adaptive Powered Joint Orthosis” corresponding to Ser. No.13/356,230; U.S. patent applications entitled “Controlling Power in aProsthesis or Orthosis Based on Predicted Walking Speed or Surrogate forSame” corresponding to Ser. Nos. 61/432,083; 13/079,564; 13/079,571;U.S. patent application entitled “Estimated Hardstop Ankle TorqueContribution Using Measurements of Bumper/Ankle Shell Deflection”corresponding to Ser. No. 61/422,873; U.S. patent application entitled“Implementing a Stand-up Sequence Using a Lower Extremity Prosthesis orOrthosis” corresponding to Ser. No. 12/872,425. International PatentApplication Nos. PCT/US2011/031105; PCT/US2012/020775;PCT/US2012/021084; and U.S. Provisional Patent Application No.61/649,640, the disclosures of each of which are hereby incorporatedherein by reference in their entirety.

In particular, concepts described herein may be guided by designprinciples that motivate use of positive force feedback, use ofintrinsic, motor damping behavior to implement dynamic clutches, andcatapult behaviors, such as those described in U.S. patent applicationsentitled “Variable-Mechanical-Impedance Artificial Legs” correspondingto Ser. Nos. 60/395,938; 10/613,499; 13/363,820, the disclosures of eachof which are also hereby incorporated herein by reference in theirentirety.

It should be understood that for those skilled in the art, the controlarchitecture described herein may be extended to bionic ankles thatemploy physical and/or SEA-applied virtual, unidirectional andbi-directional parallel elastic elements where torque-displacementcharacteristics of these systems may be calibrated before use. Further,while such control architecture(s) may be applied to a bionic ankleprosthesis, these principles may be readily extended to orthotic,exoskeletal or humanoid applications in lower-extremity augmentation ofankle, knee and hip.

While systems in accordance with the present disclosure do not requireinertial measurements as input for actuator modulation, it can beappreciated that systems described herein may be used in place of or incombination with inertial measurement systems. For instance, an actuatorresponse may be accomplished by controlling motor torque, τ_(m), in aclosed-loop or open-loop manner, to match a desired response. In such anarchitecture, joint angle, motor angle and 6-DOF inertial state(orthogonally-opposed measures of local angular rate and acceleration assampled by an Inertial Measurement Unit (IMU)) may be used to computeSEA and hardstop torque via calibrated models, to inform state machinetransitions, to estimate walking speed and/or to adapt to changes inwalking speed or terrain modality. As discussed above, SEA torque andhardstop torque may be used as input to modulate reflex parametersemployed in powered plantar flexion. Table 1 provides a summarizedmapping of the intrinsic firmware states to the level-ground, gait cyclestates as implemented in an artificial ankle device. FIG. 3 shows aschematic of an artificial ankle device that illustrates variousparameters that may be referenced in the present disclosure.

TABLE 1 Alignment of level-ground gait cycle states with intrinsicfirmware states for an embodiment. Level-Ground Intrinsic Gait CycleFirmware State State Actuator Response¹ Controlled State 4: Early τ_(m)= −k_(es)(θ − θ_(es)) − b_(es) 

Plantar Stance (ES) Flexion (CP) Controlled Suite 5: Late τ_(m) =−k_(ls)(θ − θ_(es)) − b_(ls) 

Dorsiflexion Stance (LS) (CD) Powered Plantar Flexion (PP) State 6: LateStance Power (LSP) τ_(m) = −k_(lsp)(θ − θ_(pp)) − b_(lsp) 

 + p_(ff)( 

) 

  ${{{Where}\text{?}} = \frac{\Gamma_{SEA} + \Gamma_{hs}}{\Gamma_{0}}},$  and Γ_(SEA) = Ankle torque supplied by the SEA. Γ_(hs) = Ankle torquesupplied by the flexion of the hardstop, Γ₀ = A normative peakdorsiflexion torque approximated by 1.7 Nm per kg of wearer body massestablished by an intact ankle population,

 is the estimated instantaneous walking speed, p_(ff)( 

) is the positive force feedback reflex gain, N( 

) is the reflex exponent, 

 = 

( 

) where 

 is the tibia pitch rate in late stance and θ_(pp) is the tail-springequilibrium Swing (SW) State 2: Early A biologically-derivedsecond-order response that Swing (ESW) returns the ankle joint angle,θ(t), to a position, θ_(es), where τ_(m) = −k_(esw)(θ(t) − θ₀(t)) −b_(esw)({dot over (β)} − 

) and τ_(esw) ² 

 + 2τ_(esw){dot over (θ)}₀ + θ₀ = θ_(esw) where τ_(esw) is the timeconstant of the second-order response. State 3: Late τ_(m) = −k_(es)(θ −θ_(es)) − b_(es){dot over (β)} Swing (LSW) Not Walking Non-walking τ_(m)= −b_(nw) ₁ {dot over (β)} (shorted leads damping for two seconds) StateMachine τ_(m) = −b_(nw) ₂ {dot over (β)}, programmable light damping¹Only open-Loop response is shown, where τ_(m) is the motor torque asreflected onto the joint-referenced series-elastic element via theactuator gear ratio. β is the joint equilibrium as defined by the motorposition. In a closed-loop formulation for States 4, 5, 2, 3 and 1, β isreplaced by the joint angle. θ, and τ_(m) is replaced by Γ_(SEA)—thetorque as applied by the series-elastic element via closed-loop torquecontrol. In State 6 so as to avoid a circular reference to Γ_(SEA),τ_(m) would serve as an input to dynamics that emulate muscle-tendonresponse, where 

 = f(x, τ_(m)) and Γ_(SEA) = c^(T)x, where x, f and c define thenon-linear dynamics.

indicates data missing or illegible when filed

In systems that operate under the firmware states summarized by Table 1,the State Machine employs state, transitions that are informed by timeduration within the state, actuator torque, hardstop torque, and inputsfrom the Inertial Measurement Unit (IMU). Complex measures of “jerk” andvibration applied to the z-component of the local or world-referencedacceleration are employed to detect heel or toe strike transition fromlate swing (LSW) to early stance (ES) Logic employing pitch velocity(tibia rotation in the sagittal plane) is used as a “guard” (qualifying)condition prior to applying the accelerometer-based foot strike logic.Pitch velocity, as measured at or near the entry into late stance (LS)may be used (as a surrogate) to estimate walking speed and as input fordetermining resulting reflex response parameters (p_(ff)({dot over (s)})and N({dot over (s)})) in late stance power (LSP).

Further, pitch rate or velocity may be used to inform state transitionsfrom a non-walking state machine into a walking state machine. Whilesuch an IMU-based approach may work well for normal gait cyclesinvolving locomotion (e.g., walking), such an approach might not beoptimized for non-walking type sequences, for example, those that mayoccur when the wearer is moving slowly in a confined space, movingbetween standing and sitting positions, or ascending/descending aladder. In a small percentage of such cases, a completely IMU-basedactuator may have a tendency to respond more vigorously than desired.Conversely, in situations where the wearer is running or jumping inplace, the state machine might miss an occasional transition, therebycausing the actuator response to be, in some cases, inconsistent.

The impedance response when the system is set to a non-walking statemay, at times, be constrained to be a viscous damper (e.g., have a highdamping coefficient resulting from shorting of the motor leads) for adiscrete period of time (e.g., approximately two seconds) followed by amore lightly-damped response, which is a less than natural response forthe wearer. In cases where transitions between non-walking and walkingoccur over short time intervals, the step response in viscosity maybecome less than desirable.

Considering again artificial leg devices that are programmed in abiologically-inspired manner where an IMU is not required, Table 2provides a summary for such a device. Such devices may be constructedand programmed to capture the reliance on torque-time and the use of anexponential decay so as to eliminate or reduce the abruptness that mayresult due to transition from one state to another.

TABLE 2 Alignment of level-ground gait cycle states with intrinsicfirmware states for an embodiment. Intrinsic Level-Ground Firmware StateState Actuator Response² Controlled State 4: Early τ_(m) = −k_(es)(t)(θ− θ_(es))(1 − u₁(θ − θ_(es))) − b_(es){dot over (β)} ³ Plantar Stance(ES) Where τ_(es){dot over (k)}_(es)(t) + k_(es) = k_(es) _(∞) ; θ_(es)= θ(t = 0); k_(es)(0) = 

; Flexion (CP) b_(es) = 

 for θ ≤ θ_(es) and b_(es) = 

 for θ > θ_(es) Controlled State 5: Late and u₁(x) is a unit stepfunction of x ⁴ Dorsiflexion Stance (LS) (CD) Powered Plantar Flexion(PP) State 6: Late Stance Power (LSP) τ_(m) = −k_(lsp)(t)(θ − θ_(pp))(1− u₁(θ)) − 

 + p_(ff)( 

) 

  ${{{Where}\text{?}} = \frac{\Gamma_{SEA} + \Gamma_{hs}}{\Gamma_{0}}},$  and Γ_(SEA) = Ankle torque supplied by the SEA, Γ_(hs) = Ankle torquesupplied by the flexion of the hardstop, Γ₀ = A normative peakdorsiflexion torque approximated by 1.7 Nm per kg of wearer body massestablished by an intact ankle population,

 is the estimated instantaneous walking speed, p_(ff)( 

) is the positive force feedback reflex gain, N( 

) is the reflex exponent, 

 = 

( 

), where 

 is the peak time- derivative of the SEA torque, Γ_(SEA), in late stanceand θ_(pp) is the tail-spring equilibrium;${k_{lsp}(t)}{is}{defined}{as}{\max\left( \frac{\Gamma_{SEA}}{{\theta(t)} - \theta_{pp}} \right)}$Swing (SW) State 2: Early A biologically-derived second-order responsethat Swing (ESW) returns the ankle joint angle, θ(t), to a position,θ_(esw), where τ_(m) = −k_(esw)(θ(t) − θ₀(l)) − b_(esw)( 

 − 

(t)) and τ_(esw) ² 

 + 2τ_(esw){dot over (θ)}₀ + θ₀ = θ_(esw) where τ_(esw) is the timeconstant of the second-order response. State 3: Late τ_(m) = − 

(θ − 

) − 

Swing (LSW) Where 

 = θ(t) on every time step to track the instantaneous joint angle. ²Onlyopen-Loop response is shown, where τ_(m) is the motor torque asreflected onto the joint-referenced series-elastic element via theactuator gear ratio. β is the joint equilibrium as defined by the motorposition. In a closed-loop formulation for States 4, 5, 2, 3 and 1, β isreplaced by the joint angle, θ, and τ_(m) is replaced by Γ_(SEA)—thetorque as applied by the series-elastic element via closed-loop torquecontrol. In State 6 so as to avoid a circular reference to Γ_(SEA),τ_(m) would serve as an input to dynamics that emulate muscle-tendonresponse, where 

 = f(x, τ_(m)) and Γ_(SEA) = c^(T)x, where x, f and c define thenon-linear dynamics. ³ The stiffness applied in ES is unidirectional. ⁴The damping when θ > 0 is increased to a large value to handle the casewhen θ₀ > 0.

indicates data missing or illegible when filed

To those skilled in the art it should be readily apparent that thecomputation and prediction of walking speed is not necessary. In someembodiments, the reflex parameters can be computed as a functiondirectly of the SEA torque rate without loss of generality in anotherpreferred embodiment. FIG. 4 illustrates various state transitions thatmay occur throughout two typical gait cycles—first exiting from EarlyStance into two successive heel-strike first gait cycles. Note that forconvenience, virtual state 1 is used as a representation of Early Stanceat t=∞. As described earlier, the early stance stiffness, k_(es), decaysexponentially leaving the damping, b_(es), as the dominant impedancecomponent.

Early Swing (ESW) to Late Swing (LSW) Transition

As shown in FIG. 4 , the ESW-LSW (2-3) transition may occur at a fixedtime (e.g., approximately 100 msec, between about 10 msec and about 200msec) after entry into ESW. During ESW, an overdamped, second-order,joint equilibrium trajectory is launched, that returns the ankle angle,θ, back to θ_(es)—a position at or near the neutral position so as toavoid a tripping hazard. In some embodiments, the time constant, τ_(ESW)applied in this trajectory is between about 10 msec and about 150 msec(e.g., approximately 50 msec), so as to correspond with that of anintact human ankle.

Late Swing (LSW) to Early Stance (ES) Transition

FIG. 5 illustrates an embodiment of a state transition from Late Swingto Early Stance (3-4). The embodiment shows the hardstop (Γ₁) and SEA(torque Γ_(SEA), torque rate {dot over (Γ)}_(SEA)) torque componentresponse for a heel-strike, first transition. The state and motor readyflags are also shown. In this example, the motor ready flag denotes themotor controller state. As shown in this figure, a value of −2 denotesthat an ankle trajectory is running and has not yet finished. A value of+2 denotes that the ankle trajectory has completed and that a motor coilresistance measurement is being acquired. A value of 6 denotes that themotor controller is ready to apply an impedance or respond to a newtrajectory or function command.

FIG. 6 depicts another embodiment of a state transition from Late Swingto Early Stance (3-4). Instead of a heel-strike transition, thisembodiment shows a toe-strike transition. As can be seen, a substantialdifference between the two different ground impact conditions is that inthe situation where heel-strike occurs first, the ground impact impartsa large negative torque, Γ_(SEA), and a large negative torque rate {dotover (Γ)}_(SEA), on the SEA. Whereas in the case where toe-strike occursfirst, the ground impact imparts a large positive torque, Γ_(hs),against the hardstop. As such, to detect these conditions reliably, a“guard condition” may first be applied to the state transition logic soas to reject the “noise” in Γ_(SEA) and Γ_(hs), during the swingphase—this is a result of the SEA torque applied to achieve the ankletrajectory and a possible collision with the hardstop during the timeinterval.

Accordingly, for each type of state transition, a threshold would becrossed (e.g., when the measured or sensed torque is greater than orless than a particular set torque value, within a certain period oftime) that triggers transition from one state to

Walking-Speed Referenced Reflex

The device may use the maximum, rate-of-change in SEA torque ({dot over(Γ)}_(SEA)) as measured in Late Stance as an estimation (or surrogate)for instantaneous walking speed. FIG. 10 a illustrates data that shows alinear relationship that exists between {dot over (Γ)}_(SEA) and thetibia pitch rate, ψ. The tibia pitch rate at mid-stance (after the footflat condition) is further known, through experimentation, to beproportional to leg-length normalized walking speed, as shown in FIG. 10b and as discussed in U.S. patent application Ser. No. 13/079,564. Thisestimation of walking speed may be computed just before use in LateStance Power to inform the reflex parameter modulation.

The graph shown in FIG. 10 c reports a high degree of correlation (R²)of pitch velocity vs. SEA torque rate during Late Stance that existsacross a broad population of production units and walkers (see circles),as measured in a standard walkabout test used to create a Dashboard.

Such studies have shown that

_(SEA) is not invariant across a population of wearers, even whennormalized by, for example, peak torque at a self-selected walkingspeed. So, in one embodiment, {dot over (Γ)}_(SEA) is observed for eachspecific wearer—both at the fastest achievable walking speed and at theslowest desired walking speed. At each speed, preferred values fortorque gain, p_(ff)({dot over (s)}), and torque exponent, N({dot over(s)}), may be determined by tuning—thereby determining values/ranges forvarious parameters, such as p_(ff) _(slow) , N_(slow), p_(ff) _(fast) ,N_(fast). With these parameters in hand, a basis is provided throughwhich the reflex response may be blended across a range of walkingspeeds. By replacing {dot over (s)} with {dot over (Γ)}_(SEA), thefollowing blended reflex equations may be used:

Method I: Blended Torque Models

? ? ? ? ? ? ? ?indicates text missing or illegible when filed

Method II: Blended Coefficients

? ?indicates text missing or illegible when filed

Where

{tilde over (P)} _(ff)({dot over (Γ)})=c ₁({dot over (Γ)})P _(ff)({dotover (Γ)}_(slow))+c ₂ P _(ff)({dot over (Γ)}_(fast))

and

Ñ({dot over (Γ)})=c ₁({dot over (Γ)})N({dot over (Γ)}_(slow))+c ₂ N({dotover (Γ)}_(fast))

where c₁ and c₂ are defined as in Method I.

Where the subscript, SEA, on {dot over (Γ)}_(SEA), is removed tosimplify the notation.

Device Extensions

It should be appreciated that while device control architectures inaccordance with the present disclosure have been applied to anartificial (bionic) ankle device with a hardstop, the hardstopfunctionality may be replaced by a physical, unidirectional orbi-directional element, parallel elastic element, a virtual.SEA-applied, parallel elastic element, or other suitable component. Forexample, in either case the hard stop torque, Γ_(hs), may be replaced bya parallel elastic element torque, Γ_(PE), where Γ_(PE) is calibrated inmanufacturing to determine the torque displacement characteristics ofthe physical or virtual elasticity.

Further, while device control architectures described herein have beenapplied to artificial ankle prostheses, concepts presented here may beextended for application in orthotic, exoskeletal, humanoid ankles, orother appropriate devices. And, while the device control architecturesherein have been applied to artificial ankle applications, thetechniques applied here may also be extended for use in accordance withother lower-extremity applications, for example, in the knee and hip.

Further Embodiments and their Implementation for Prosthetic or OrthoticAnkle Devices

Embodiments of bionic leg devices, such as the BiOM^(T2) system producedby iWalk, Inc., may employ five states—Early Stance (ES; State 4), LateStance (LS; State 5), Late Stance Power (LSP; State 6), Early Swing(ESW; State 2) and Late Swing (LSW; State 3)—that align with the humanbiomechanical gait cycle states controlled plantar flexion (CP),controlled dorsiflexion (CD), powered plantar flexion (PP), Early Swing(ESW) and Late Swing (LSW), respectively. The present disclosure reviewsvarious details of control actions within each state and describes thestate transition logic that causes entry into the state.

Early Stance (ES) Control Action In ES (State 4), for some embodiments,the SEA applies a lightly-damped, torsional spring response inaccordance with the human biomechanical joint response in ControlledPlantar Flexion. The impedance as applied by the SEA motor torque, τ_(m)is comprised of a time-varying spring, k_(es)(t), and a time-varyingdamping component, b_(es)(t). The “virtual spring” joint equilibrium,θ_(es), is the ankle angle as captured at ES entry. In some cases, oneor more variables (e.g., spring constant, damping component, jointequilibrium, gain, exponent, etc.) of the motor torque may betime-dependent and/or may exhibit a time decay-type behavior (e.g.,exponential, linear, piecewise, etc.). The actuator may apply anexponential decay to the stiffness component in order to make the ankleincreasingly more compliant as the state progresses—to emulate humanbiomechanics while walking slowly, including on steep or uneven terrain.The ES control action may be modeled as follows:

? ?indicates text missing or illegible when filed

whereτ_(m) is the motor torque,θ is the joint angle.β is the SEA motor angle,And where,τ_(es)k_(es)(t)+k_(es)(t)=k

applies an exponential stiffness decay with time constant, τ_(es)θ_(es)=θ(t=0),In some embodiments, the following second-order relation may be used tomodel exponential stiffness decay:

τ

² {umlaut over (k)} _(es)(t)+2r

{dot over (k)} _(es)(t)+k _(es)(t)=k

t=time since ES entry

k

(0)=k

b

(0)=b _(es) ₀

To those skilled in the art, other linear or non-linear differentialequations can be applied to accomplish this decay function.As provided in the equation above, the stiffness decays to k

with a time constant, τ_(ES)—e.g., about 200 milliseconds, or between100-500 milliseconds. In some embodiments, the time constant may be set(e.g., optimized) so as to allow the ankle to conform to the groundsurface while the wearer walks slowly down an incline.Examples of these are included in Table 3 below.

Early Stance (ES) Entry State-Transition Details Late Swing(LSW)-to-Early Stance (ES) Transition

In some embodiments, the state transition into ES from LSW may occurwhen a foot-strike is detected—for example, by presence of a large orincreasing heel load (L

or L

, respectively) as measured by Γ_(SEA) is a large toe load (L

) as measured by Γ_(hard stop); or the extended presence of a largeankle load (L₃₋₄ ₀ ) as measured by Γ_(ankle). That said, to detectthese conditions reliably, a “guard condition” may first be applied tothe logic to reject any such noise in Γ_(SEA) and Γ_(hard stop) that mayarise during the swing phase. This may be a result of the SEA torqueapplied to achieve the ankle trajectory and a possible collision withthe hardstop during the time interval. The LSW-ES guard logic (GUARD)may be implemented as follows:

GUARD=((t

<100 msec) AND (Γ_(hard stop)<0.58Γ₀)) OR ((t

<250 msec) AND (TransitionEnabled=FALSE) AND (Γ_(hard stop)<0.58Γ₀))

Or, alternatively, the GUARD logic may be employed according to thefollowing relation:

GUARD=((t

<100 msec) AND (Γ_(hard stop)<0.58Γ₀)) OR ((t

<250 msec) AND (AnkleNotReturned=TRUE) AND (Γ_(hard stop)<0.58Γ₀))

In the event that GUARD is FALSE, the LSW to ES state transition (3-4)logic may be as follows:

L ₃₋₄ =L

OR L

OR L

OR L

where

-   -   L₃₋₄ _(A) : (Γ_(hard stop)>45 Nm) AND    -   (Γ_(hard stop)(t)−Γ_(hard stop)(1-40 msec>11 Nm).    -   L₃₋₄ _(B) : (min(Γ        ) detected) AND    -   (Motor is in the READY state) AND    -   ({dot over (Γ)}_(SEA)<−50 Nm/s) AND    -   (Γ_(SEA)<min(Γ        )−2 Nm).    -   L₃₋₄ _(C) : (min(Γ_(SEA)) detected) AND    -   ({dot over (Γ)}_(SEA)<−180 Nm/s) AND    -   (Γ        <min(Γ        )−1 Nm) AND    -   (Γ_(SEA)(t)−Γ_(SEA)(t−8 msec)<−0.5 Nm) AND    -   (Γ_(SEA)(t)−Δ_(SEA)(t−10 msec)<−1.0 Nm).    -   L₃₋₄        :(t_(LSW)>1500 msec) AND    -   (TrasitionEnabled=TRUE) AND    -   (Γ_(ankle)(t)>30 Nm)∨t where t_(LSW)−300 msec<t≤t_(LSW).        where    -   t_(LSW) is the elapsed time since LSW entry.    -   Γ_(SEA)(t), and Γ_(hard stop)(t) are the SEA and Hard Stop        torque at time, t, respectively, READY is a signal indicating        that the motor controller processor has completed the trajectory        return,    -   Transition Enabled is a motor state indicating that the motor        controller has completed the trajectory return instruction and        that the motor temperature measurement has been completed.    -   AnkleNotReturned is a check to indicate whether the ankle has        returned to an initial state and has suitably dorsiflexed.    -   min(Γ        ) is the first validated minimum, of SEA torque while        GUARD=FALSE.    -   {umlaut over (Γ)}        is notation for the mean of Γ_(SEA) computed using samples from        the prior n milliseconds referenced to the current time, t.    -   Γ_(ankle)(t)=Γ_(SEA)(t)+Γ_(hard stop)(t) is the total ankle        torque.

For various embodiments presented herein, it is noted that the ES, LS,LSP, ESW and LSW control response may be invariant with respect to whichlogic condition—L₃₋₄ _(A) , L₃₋₄ _(B) , L₃₋₄ _(C) or L₃₋₄ _(D) —causesthe state transition into ES.

Late Stance (LS)-to-Early Stance (ES) Transition

In some cases, for instance, when the wearer stops in mid-stance, thecontrol system may transition from LS (State 5) back to ES (State 4), sothat the ankle state responds in accordance with the true walking cyclestate. The L₅₋₄ transition may be informed by a negative change inΓ_(SEA) after the elapsed time in LS exceeds 500 msec and may besummarized as follows:

L ₅₋₄=((Γ_(SEA)(L _(LS))−max_(LS)(Γ_(SEA)))<−5 Nm) AND ((Γ_(SEA)(t_(LS))−Γ_(SEA)(t _(LS)−10 msec))<−0.5 Nm) AND (t _(LS)>500 msec)

where

-   -   t_(LS) is the elapsed time since entering LS    -   max_(LS)(Γ_(SEA)(t)) is the maximum value of Γ_(SEA)(t) in LS.

Early Stance (ES)-to-Early Stance (ES) Transition

In some cases, for instance, when the wearer stops in ES then begins towalk again, the impedance and equilibrium are reset to appropriatevalues for foot strike to occur. Accordingly, the device may beconfigured to re-enter the ES state based upon detection of an L₄₋₁transition. This transition may be informed by a negative change isΓ_(SEA) after the elapsed time in ES exceeds 500 msec, and may besummarized as follows:

L ₄₋₄=((Γ_(SEA)(t _(ES))−max_(ES)(Γ_(SEA)))<−5 Nm) AND((Γ_(SEA)((Γ_(SEA)(t _(ES))−Γ_(SEA)(t _(ES)−10 msec))<−0.5 Nm) AND (t_(ES)>500 msec)

where

-   -   t_(ES) is the elapsed time since entering ES    -   max_(ES)(Γ_(SEA)(t)) is the maximum value of Γ_(SEA)(t) in ES.

Late Stance Power (LSP)-to-Early Stance (ES) Transition

In some cases, the entry into ES from LSP may occur if the ankle isback-driven into LSP (LSPRegen)—to protect the wearer in the event thatthe state machine does not detect a walking state transition out of LSP,for example, to ESW. Because there is no stiffness in opposition to aplantar flexion displacement in LSP, the expected ES impedance(heel-strike stiffness) may be absent in a heel-strike event and wouldthereby surprise the wearer. That is, if there is no stiffness in theankle after LSP occurs, the system may, by default, set its parametersto the ES stance in preparation for the device in striking the ground.

LSP-to-ES “LSPRegen” Transition

The LSP-ES LSPRegen transition may occur when L₆₋₄ _(LSPRegen) =TRUE perthe logic equation:

L

=GUARD_(Regen) AND L

GUARD_(Regen)=(max_(LSP)Γ_(SEA)−Γ_(SEA)(0)<10 Nm)

L

={dot over (Γ)}_(SEA)(t)<−150 Nm AND (Γ_(SEA)(t)−Γ_(SEA)(t−10 msec)<−1.2Nm AND Γ_(hard stop)(t)<1 Nm

where

-   -   t=t_(LSP) is the elapsed time in LSP and    -   max_(LSP)Γ_(SEA) is the maximum value of the SEA torque since        entry into LSP.

Late Stance (LS) Control Response

In various embodiments of a controller for artificial leg devicespresented herein, LS (State 5) bridges the control response between ESand LSP—typically between foot flat and hard stop engagement. In LS, theactuator continues to apply a damped, torsional, spring response so asto correspond with the early CD response in human biomechanics.Mathematically, the LS response is captured in Eq. 0.1.

It is well-understood that the spinal reflex arc connecting the Achillestendon stretch and the soleus (calf) muscle contraction employs positiveforce feedback—both torque and torque derivative are employed to amplifythe reflex response in the contractile element (muscle). To mimic thisreflex arc in artificial leg devices according to the presentdisclosure, the peak rate of change of ankle torque in LS. {dot over(Γ)}

, may be used as input for the strain-rate component of the reflex andspring dynamics applied in LSP by the SEA itself the bionic, artificialmuscle-tendon unit in the BiOM ankle. Here,

{dot over (Γ)}

={c _(SEA) max

({dot over (Γ)}_(SEA))+c

max

({dot over (Γ)}_(hard stop))}

  (1)

where

-   -   max        (⋅) denotes the maximum of a function during LS

? ? ?indicates text missing or illegible when filed

and

-   -   ∫        (⋅)dt denotes the time integral over LS.

Late Stance (LS) Entry State-Transition Details

In some embodiments, ES entry into LS (State 5) is the only statetransition into LS. The LS transition may occur if either a large toeload (L₄₋₅ _(A) ) or heel load (L₄₋₅ _(B) ) is sensed by Γ_(hard stop)and Γ_(SEA) respectively. An example of the mathematical formulation ofthe state transition (4-5) is described below.

L ₄₋₅ =L ₄₋₅ _(A) OR L ₄₋₅ _(D)

where

? ? ?indicates text missing or illegible when filedL ₄₋₅ =L ₄₋₅ _(A) OR L ₄₋₅ _(B)

Where

? ? ?indicates text missing or illegible when filed

It should be appreciated that the control response in LS, LSP, ESW andLSW may be invariant with respect to which logic condition—L₄₋₅ _(A) orL₄₋₅ _(B) —causes the 4-5 transition.

Late Stance Power (LSP) Control Response

In some embodiments, the actuator response in LSP (State 6) is comprisedof two terms—a unidirectional torsional spring, k_(lsp), withequilibrium at a torque-rate-dependent plantar flexion angle, θ_(pp),and a torque-rate-dependent reflex. The reflex term applies a positiveforce-feedback response that comprises two components—a torque-ratedependent gain, p_(ff)({dot over (Γ)}_(ankle)

), and a non-linear, normalized joint torque feedback,

? ?indicates text missing or illegible when filed

with a torque-rate dependent exponent, N({dot over (Γ)}_(ankle)

). In some embodiments, the torque gain may range between 0 and 200 Nm,and the torque exponent may range between 1 and 5. Here, {dot over(Γ)}_(LS) is the peak rate of change of joint torque in LS, as describedin the previous section that addresses late stance. Both p_(ff) and Nmay be piecewise-continuous, linear functions, defined each by theirvalues at a slow speed and a high speed torque rate—{dot over(Γ)}_(ankle)

_(slow) and {dot over (Γ)}_(ankle)

_(fast) respectively. At torque rates beyond this range both p_(ff) andN may be held constant. In some embodiments, p_(ff) and/or N aretime-dependent functions, for example, that exhibit an exponential decaybehavior.Mathematically, the LSP control response may be defined in Equation 2,shown below.

? ?indicates text missing or illegible when filed

where

-   -   τ_(m) is the SEA motor torque    -   k_(lsp) _(max) is a torsional spring stiffness defined as the        maximum of a quantity equal to the torque-rate dependent reflex        torque divided by the value of θ−θ_(pp),    -   θ_(pp) is a plantar flexed torsional spring equilibrium that is        a piecewise, continuous linear function of {dot over        (Γ)}_(ankle)    -   p_(ff) and N are each a piecewise, continuous linear function of        {dot over (Γ)}_(ankle)        as defined above, or may be time-dependent functions that may        range between 0-200 Nm and between 1-5, respectively.

? ?indicates text missing or illegible when filed

is the normalized ankle torque

where

-   -   Γ₀ is a normalizing torque equal to

? ?indicates text missing or illegible when filed

-   -   where m_(wearer) is the wearer mass in kilograms.

In some cases, one or more of the parameters of an actuated torque aretime-dependent functions that exhibit time-decay behavior (e.g.,exponential, linear, piecewise, etc.). For instance, k_(pp), θ_(pp),p_(ff) and/or N may exhibit exponential decay behavior over time, so asto provide for a soft reflex response or gradual joint equilibriumtransitions. As an example, during LSP, the wearer may decide thathe/she would like to ease in or out of powered plantar flexion. If thegain and/or exponent of the torque reflex response exhibitstime-dependent decay, the wearer may experience a relatively smoothreflex response than may otherwise be the case without the decaybehavior. Or, θ_(pp) may also exhibit time-dependent decay behavior,resulting in relatively smooth transitions from one state to another.Any suitable time-dependent behavior may be employed, such as thosefunctions described for various embodiments of the present disclosure.FIGS. 24-25 show examples of suitable reflex parameter modulationrelationships.

Late Stance Power (LSP) Entry State-Transition Details

In some embodiments, the IS to LSP transition (5-6) may occur when thetoe load torque exceeds a programmable threshold. Mathematically, theL₅₋₆ transition may occur when Γhard stop>5 Nm.

Early Swing Control Response

In some embodiments, the ESW (State 2) control response of theartificial leg device mimics the damped, second-order, spring-massresponse of the early swing phase in human walking biomechanics—thisresponse restores the ankle from the toe-off position at the terminus ofpowered plantar flexion to its neutral position, in anticipation of thefoot strike in the next gait cycle. Typically, the time constant,τ_(esw), of this response is approximately 50 milliseconds, but may varyappropriately.

In ESW, an overdamped, second-order equilibrium trajectory, θ₀(t), maybe applied to return the joint to a fixed neutral position, θ_(esw)—aposition that may be invariant to all biomechanical modalitiesincluding, but not limited to, terrain, walking speed, and toe-offangle. A damped (b_(esw)) and spring (k_(esw)) impedance may be appliedin relation to this equilibrium trajectory. Feedforward of the estimatedmotor torque may be used to eliminate response lag due tomotor/drive-train inertia and damping. The mathematical formulation ofthe ESW control response with inertia-only feedforward may be summarizedin Equation 3 shown below.

$\begin{matrix}\text{?} & (3)\end{matrix}$ ? ?indicates text missing or illegible when filed

where

-   -   τ_(m) is the SEA motor torque,    -   τ        is the time constant of the over-damped, second-order response,    -   θ        (0) is the toe-off angle, initialized to θ(t) at ESW entry (LSP        Exit),    -   β is the SEA motor angle reflected at the ankle joint and    -   θ_(esw) is the invariant, neutral position destination for all        ESW trajectories    -   J        is the motor inertia reflected onto the joint

Early Swing (ESW) Entry State Transition Logic

Transitions into ESW may normally originate from LSP, as described inthe following section that addresses the late stance power to earlyswing transition. Transitions into ESW can originate from ES when thewearer lifts the foot oil the ground, as described in the section thataddresses ES-to-ESW at Foot-off.

Late Stance Power (LSP)-to-Early Swing (ESW) Transition

The LSP-ESW transition may be defined by either a toe-off (L₆₋₂_(toe-off) ) or a foot-off event (L₅₋₂ _(foot-off) ) while in LSP.

LSP-to-ESW at Toe-Off

Toe-off may occur when the ankle torque, Γ_(ankle), drops below athreshold close to zero.

The following guard, pre-trigger, and state transition conditions may beapplied in succession to accomplish the LSP-ESW (6-2) transition bytoe-off

Toe-Off Guard Condition Details

The LSP-ESW by toe-off transition may be halted until GUARD hastransitioned from TRUE to FALSE.

GUARD=(t _(lsp)<200 msec) AND (Γ_(hard stop)>0 OR {dot over (Γ)} _(SEA)

>−200 sec/Nm OR max_(lsp)(Γ_(hard stop))<20 Nm)

Toe-Off Pre-Trigger Details

Before detecting the LSP-ESW toe-off transition, compute the following:

ToeOffTransitionEnable=Γ_(ankle)<0.5 max_(lsp)(Γ_(hard stop)(t)) ANDΓ_(ankle)<25 Nm if ToeOffTransitionEnable=TRUE=True then capture t_(enabled)

Toe-Off Transition (6-2) Logic

L ₆₋₂

=ToeOffTransitionEnable AND (Γ_(ankle)<10 Nm OR t−t _(enabled)≥20 msec)

where in the above,

-   -   t_(lsp) is the time since LSP entry    -   max_(lsp)(Γ_(hard-step)(t)) is the maximum value of hard stop        torque in LSP prior to t_(lsp)    -   {dot over (Γ)} _(SEA)        is the mean value of SEA torque rate over the past 10        milliseconds.        As a result, the LSP to ESW transition can occur when L₆₋₃ is        TRUE.

LSP-to-ESW at Foot-Off

The “foot-off” condition—L₆₋₂

—may be informed by a rapid drop in both SEA and Hard Stop torque, whichmay be summarized as follows:

L ₆₋₂

=(L ₆₋₂

OR L ₆₋₂

OR L ₆₋₂

OR L ₆₋₂

) AND (t _(lsp)>1600 msec)

L ₆₋₂

=Γ_(SEA)<0 AND Γ_(SEA)(t)−Γ_(SEA)(t−10 msec)<−1 Nm AND Γ_(hard stop)<30Nm AND Γ_(hard stop)(t)−Γ_(hard stop)(t−40 msec)<−11 Nm

L ₆₋₂ _(foot-off) ={dot over (Γ)}_(SEA)<−180 Nm/sec AND Γ_(hard stop)<30Nm AND Γ_(hard stop)(t)−Γ_(hard stop)(t−40 msec)<−5 Nm

L ₆₋₂

={dot over (Γ)}_(SEA)<−50 Nm/sec AND Γ_(hard stop)<30 Nm ANDΓ_(hard stop)(t)−Γ_(hard stop)(t−40 msec)<−11 Nm

L ₆₋₂

={dot over (Γ)}_(SEA)<−50 Nm/sec AND Γ_(hard stop)<50 Nm ANDΓ_(hard stop)(t)−Γ_(hard stop)(t−40 msec)<−22 Nm

where

-   -   t=t_(LSP) is the elapsed time since entry into LSP

ES-to-ESW at Foot-Off

The “foot-off” condition—L₄₋₂ _(foot-off) —may be informed by a rapiddrop in SEA and Hard Stop torque, as follows:

L ₄₋₂ _(foot-off) =GUARD_(foot-off) AND {L ₄₋₂

OR L ₄₋₂

OR L ₄₋₂

OR L ₄₋₂

}

Guard_(foot-off)=FromLSPRegen OR t

<800 msec

L ₄₋₂

=Γ_(SEA)<0 AND Γ_(SEA)(t)−Γ_(SEA)(t−10 msec)<−1 Nm AND Γ_(hard step)<30Nm AND Γ_(hard stop)(t)−Γ_(hard stop)(t−40 msec)<−11 Nm

L ₄₋₂

={dot over (Γ)}_(SEA)<−180 Nm/sec AND Γ_(hard stop)<30 Nm ANDΓ_(hard stop)(t)−Γ_(hard stop)(t−40 msec)<−5 Nm

L ₄₋₂

={dot over (Γ)}_(SEA)<−50 Nm/sec AND Γ_(hard stop)<30 Nm ANDΓ_(hard stop)(t)−Γ_(hard stop)(t−40 msec)<−11 Nm

L ₄₋₂

={dot over (Γ)}_(SEA)<−50 Nm/sec AND Γ_(hard stop)<50 Nm ANDΓ_(hard stop)(t)−Γ_(hard stop)(t−40 msec)<−22 Nm

where

-   -   t=t_(ES) is the elapsed time since entry into ES,    -   FromLSPRegen is a flag set in ES to note that ES entry        originated from LSP during an unexpected regeneration event in        powered plantar flexion,    -   GUARD_(foot-off) is a guard logic condition that blocks the        transition if ES entry originated from the excessive        regeneration event in LSP or if the elapsed time within ES is        less than a pre-specified duration (800 milliseconds).

Late Swing (LSW) Control Response

In LSW after the ESW return to the neutral angle is completed, the SEAapplies a lightly-damped, torsional spring response equivalent to thatapplied at ES entry. This ensures that the intended impedance to beapplied at foot strike is instantiated before impact—thereby achievingresponse continuity that is insensitive to ES state transition delay.The mathematical formulation of the LSW response is captured in Equation4.

$\begin{matrix}\text{?} & (4)\end{matrix}$ ?indicates text missing or illegible when filed

where

-   -   θ        =θ(0)    -   β is the motor angle as projected onto the joint angle from SEA        kinematics

In LSW, after the ESW return to the neutral angle is completed, the SEAmay apply a lightly damped, torsional spring response—with a springconstant, k_(es)(t) that may be designed to decay exponentially,according to a second-order differential equation. Such a decay, whilenot limited to exponential behavior, may help to ensure that theintended impedance to be applied at foot strike is instantiated beforeimpact—thereby achieving foot-strike response continuity that isinsensitive to ES state transition delay. Such a form of decay dynamicshas the emergent property that stiffness decreases with increasedwalking speed. This property acts to reduce foot-strike stiffness whilewalking slowly down a steep slope, for instance. The joint equilibrium,θ

, may be set to the ankle angle, at entry, θ(0). The mathematicalformulation of the LSW response, including stiffness decay dynamics, iscaptured in the Equations 5 and 6 below.

$\begin{matrix}\text{?} & (5)\end{matrix}$ $\begin{matrix}\text{?} & (6)\end{matrix}$ ?indicates text missing or illegible when filed

Where

-   -   t is the time elapsed since LSW entry    -   θ        =θ(0), the value at LSW entry    -   b        is the fixed value of damping    -   β is the motor angle as projected onto the joint angle from SEA        kinematics    -   τ_(h)        controls the stiffness decay, typically 200 milliseconds    -   k        (0)=k_(es)    -   k_(es)        is the terminal value of stiffness

Late Swing (LSW) Entry State-Transition Details

The ESW-LSW state transition may occur when the motor control processorreports that it is READY, thereby signifying that the ESW trajectory iscompleted. OR, for example, when L

<100 msec.

Late Swing (LSW) Entry from Early Stance (ES)

An ES-LSW transition can occur in cases where alter an extended periodin ES (e.g., approximately two seconds) a possible ground impact ispresent as detected by a toe load (L₃₋₄ _(A) ), toe unload (L₃₋₄ _(B) ),or footstrike (L₃₋₄ _(C) ), as provided below.

-   -   L₄₋₃ _(A) : Toe-Load Detected        -   (Γ_(hard stop)>45 Nm) AND        -   (Γ_(hard stop)(t)−Γ_(hard stop)(t−40 msec)>11 Nm).    -   L₄₋₃ _(B) : Toe-unload Detected        -   (min(Γ_(SEA)            ) detected) AND        -   (Motor is in the READY state) AND        -   ({dot over (Γ)}_(SEA)<−50 Nm/s) AND        -   (Γ_(SEA)<min(Γ_(SEA)            )−2 Nm).    -   L₄₋₃ _(C) : Foot-Strike Detected        -   (min(Γ_(SEA)            ) detected) AND        -   ({dot over (Γ)}_(SEA)<−180 Nm/s) AND        -   (Γ _(SEA)            <min(Γ_(SEA)            )−1 Nm) AND        -   (Γ_(SEA)(t_(es))−Γ_(SEA)(t_(es)−0 msec)<−0.5 Nm) AND        -   (Γ_(SEA)(t)−Γ_(SEA)(t−10 msec)<−1.0 Nm).            -   Where                -   t_(es) is the elapsed time since ES entry,    -   Γ_(SEA)(t), and Γ_(hard stop)(t) are the SEA and hard stop        torque at time, t, respectively,    -   READY is a motor state indicating that the motor controller        processor is ready to accept commands.    -   min(Γ_(SEA) _(es) ) is the first validated minimum of SEA torque        after ES entry.

While description for each of the state transitions is provided above.Table 3 summarizes the state transition logic, including variousnon-limiting conditions and thresholds that are used for an embodimentof an artificial leg device, in accordance with the present disclosure.FIG. 11 provides a schematic that illustrates operation of an embodimentof an artificial leg device.

TABLE 3 State transition setup for an embodiment of an artificial legdevice. State Machine Transitions and Threshold Setup State & ThresholdThresholds Transition Transition Conditions Setting values notes InSTATE 1 Power On Systems Initializing; {short motor leads; Check batterypowery etc.} 1 −> 3 Systems initialization completed! AND Ks torquevalue −35 Nm to 10 Nm 10 Nm > Ks_torque > −35 Nm In STATE 2 Setup motorswing Impedance control{ } 2 −> 3 Timer > 100 ms Local Timer 0.1 secTime period given for foot return In STATE3 On entry{updateHS_torque_Thr}; Setup impedance_control; Shut_down_check; 3 −> 4 Guard -(Timer < 0.1 sec)AND Timer 0.1 sec min time period in 4; No(Ankle_Torque < 0.58 PCI) Large Ankle Load 058 PCI Large ankle load toTransition see foot on ground; (Timer < 0.25 sec) AND Timer 0.25 secShort time period in 3; (transition NOT enabled) AND Motor_ready_flag0.58 PCI Motor NOT ready (ankle_Torque < 0.58 PCI) Large Ankle Load(ankle returned, temperature measured); Large ankle load to see foot onground; Transitions (1^(st)_min Ks_torque found) AND Ks torque rate −180Nm/s Min Ks Torque found (Ks_torque_dot < −180 Nm/s) ANDKs_torque_changes_6 ms −0.5 Nm/6 ms  at beginning of 3 Ks:(Ks_torque_rising_6 ms < 0.5 Nm) AND Ks_torque_changes_10 ms  −1 Nm/10ms torque reduced in (Ks_torque_rising_10 ms < −1 Nm) ANDKs_torque_drops_from −1.0 Nm fast speed (Ks_torque_6 ms_mean-1^(st) minmin position Ks torque drops in Ks_torque < −1 Nm) 6 ms period Ks torquekeeps dropping in 10 ms Ks torque drops from its min position(1^(st)_min Ks_torque found) AND Ks torque rate  −50 Nnm/s-2.0 Nm Min KsTorque found (motor ready flag re-settled) AND Ks_torque_drops_from atbeginning of 3 HS: (Ks_torque_dot < −50 Nm/s) AND min position torqueNOT rising; (Ks_torque_6 ms_mean-1^(st) min Ks torque Ks_torque < −2 Nm)reduced in moderate speed; Ks torque drops big from its min position (HStorque > HS_torque_Thr) Hard Stop Torque 25 Nm to 45 Nm Protect 3 countAND (HS torque_rising in 40 ms > 11 Nm) HS torque rate_mean drift onankle  11 Nm/40 ms encoder; varying based on user weight; Protect slowloading. case; (Timer > 1.5 sec) AND Local Timer 1.5 sec Long enough in3; (transition enabled ) AND Ankle Torque 30 Nm Ankle loaded (>2 (ankleTorque > 30 Nm) AND Timer_High Load 0.3 sec encoder counts); (High AnkleTorque Timer > 0.3 sec) Ankle Loaded long to see foot on ground; InSTATE 4 On Entry (Check_battery_power; Read_motor_temperature;)Setup_decay_impedance_control; Update_Ks_torque_changes;Update_maximum_Ks_torque; Shut_down_check; 4 −> 5 HS_torque > 0.58 PCIHard stop torque 0.58 PCI Large Hard stop load (HS_torque >HS_torque_Thr)AND Hard Stop Torque 25 to 45 Nm Ankle loaded; (HStorque_rising in 40 ms > 11 Nm) HS torque rate_mean  11 Nm/40 ms Ankleloaded fast; (HS_torque < 15 Nm) AND Hard stop Torque −5 Nm Hard stopNOT loaded; (Ks_torque_max_drops_from_entry < −5 Nm) AND Ks torque maxdrops in 4 0.10 Nm/s Ks torque drops big to confirm foot strike;(Ks_torque_dot > 0) AND ks_torque_rate Positive Ks torque rates toconfirm (Ks_torque_dot_10 ms_mean > 10 Nm/s Ks_torque_rate_10 ms_meanfoot flat happened; 4 −> 4 (Timer > 0.5 sec) AND Timer 0.5 sec Max timein 4 normally; (Ks_torque_drops_in_10 ms < −0.5 Nm) ANDKs_torque_changes_10 ms −0.5 Nm/10 ms  To see Ks torque changingdirection; (Ks_torque_max_drops_from_entry < −5 Nm) Ks torque max dropsin 4 −5 Nm Ks torque drops big to confirm foot strike; 4 −> 2 Guard -State 6 to 4 protection ON This state 4 was transitioned from NO state 6transition Timer < 0.8 sec Timer 0.8 sec Must stay in 4 long enoughFoot: (HS_torque_40 ms_Ago < 30 Nm) AND Hard Stop Torque 40m s ago 30 NmLow Hard stop torque; unloading (HS_torque_drops_in_40 ms < −5 Nm) HardStop Torque drops  −5 Nm/40 ms Hard stop torque drops to see detectorAND (Ks_torque_dot < −180 Nm/s) moderately −180 Nm/s unloading;Transitions: Ks torque rate Ks torque reduced in fast speed to seeunloading (HS_torque_40 ms_Ago < 30 Nm) AND Hard Stop Torque 40 ms ago30 Nm Low Hard stop torque; (HS_torque_drops_in_40 ms < −11 Nm) AND HardStop Torque drops −11 Nm/40 ms Hard stop torque drops to see(Ks_torque_dot < −50 Nm/s) fast −50 Nm/s unloading; Ks torque rate Kstorque reduced in moderate speed to see unloading (HS_torque_40 ms_Ago <30 Nm) AND Hard Stop Torque 40 ms ago 30 Nm Low Hard stop torque;(HS_toque_drops_in_40 ms < −11 Nm) AND Hard Stop Torque drops fast −11Nm/40 ms Hard stop torque drops to see (Ks_torque_rising_10 ms < −1 Nm)AND Ks_torque_changes_10 ms 0 Nm unloading; (Ks_torque < 0 Nm) Ks torqueKs torque keeps dropping in 10 ms Ks torque is low Transitions:(HS_torque_40 ms_Ago < 50 Nm) AND Hard Stop Torque 40 ms ago 50 Nmmoderate Hard stop torque; (HS_torque_drops_in_40 ms < −22 Nm) AND HardStop Torque drops −22 Nm/40 ms Hard stop torque drops very fast(Ks_torque_dot < −50 Nm/s) very fast −50 Nm/s to see unloading; Kstorque rate Ks torque reduced in moderate speed to see unloading InSTATE 5 Update_extreme_Torque_rate, Update_Ks_torque_changes;Setup_decay_impedance_control; Shut_down_check; On Exit {Blend_torque_rate; Blend_reflex_Coeff; Blend_tail_spring;} 5 −> 6MS_torque > 5 Nm Hard Stop Torque 5 Nm Hard stop triggered 5 −> 4(Time > 0.5 sec) AND Timer 0.5 sec Max time in 5 normally;(Ks_torque_rising_in_10 msc < −0.5 Nm) Ks_torque_changes_10 ms −0.5Nm/10 ms  To see Ks torque changing direction; AND Ks_torque_max_changes−5 Nm To see foot strike for sure; (Ks_torque_drops_from_max_in_5 < −5Nm) In STATE 6 Detect_peak_ankle_moment;Detect_significant_reflex_action; Update_motor_command_torque (torque,tailSpring, temperatureFactor, ForceField): Shut_down_check; 6 −> 2Guard - (Timer < 0.2 sec) AND Timer 0.2 sec Min Time in state 6normally; No ((maxHS_torque < 20 Nm) OR Max HS torque 20 Nm Hard stopNOT engaged; Transition (HS torque > 0) OR HS torque 0 Nm Hard stopstill touching: (KS_torque_dot_10 ms_mean > −200 Nm/s)) Mean Ks tonguerate in 10 ms −200 Nm/s Ks Not released; Transitions (Timer > 1.6 sec)AND Timer 1.6 sec Max time allowed in state 6 (foot_unloading_detector)If Low ankle torque 25 Nm (ankle_Torque < 0.5*PeakTorque) AND(ankle_torque < 25 Nm) low ankle torque Acknowledged; Timer_delayed ++End Transitions: Ankle total torque 10 Nm Ankle load released;(ankleTorque < 10 Nm) OR Low ankle Torque Timer 0.02 sec Stayed longenough at low ankle (Timer_delayed >= 0.02 sec) torque level; 6 −> 4(maxKs_torque_rising_from_entry_in_6 < 10 Nm) ANDmaxKs_torque_rising_from_entry_in_6 10 Nm No reflex detested; (HS torque< 1 Nm) AND 1 Nm Hard stop NOT triggered: (Ks_torque_rising_in_10 ms <−1.2 Nm) AND Hard Stop Torque −1.2 Nm/10 ms  Last two conditions to seefoot strike (Ks_torque_dot < −150 Nm/s) Ks_torque_changes_10 ms −150Nm/s for sure ; Ks_torque_rate

Embodiments of the present disclosure may include a multi-modal controlsystem for an artificial leg device having series and parallelelasticactuator-based muscle-tendon units (MTU) at the ankle and knee formodulation of joint impedance, joint equilibrium and reflex torque, inaccordance with locomotion modality, gait cycle phase within thatmodality and cadence; a plurality of metasensors for intra-gait cycledetermination of terrain modality, ground reaction force and zero-momentpoint, and external load-bearing influence; an intent recognitionprocessor that employs the metasensor data to infer locomotion modalityand the transitions between these; and a biophysically-inspired statecontrol processor that employs MTU torque and derivatives, metasensorstate and intent recognition output to accomplish transitions betweenthe joint-based state machines.

The bionic architecture may restore function per normative measures ofmetabolic cost-of-transport and gait mechanics, including jointkinematics and kinetic measures. The architecture may further optimizebattery economy and achieve safe operation in the event of power lossthrough use of tuned series-elastic elements and regenerative dynamicclutching (braking) functions in the joint MTU controls. The multi-modalarchitecture herein can be broadly applied to lower extremityaugmentation systems—including powered prosthetic and orthotic legsystems, exoskeletons, and exomuscle-tendon units—and humanoid robotsthat actuate the ankle, knee and hip.

FIG. 12 illustrates elements of another embodiment of a bionic legsystem architecture in accordance with the present disclosure. In theembodiment shown, the system includes series-elastic actuators (SEA)serving as bionic muscle-tendon units (MTU) at the ankle and knee; anankle socket-mounted force/torque sensor to measure axial force,sagittal plane moment and coronal plane moment; a state controlprocessor that embodies a gait cycle state machine, modulates MTUresponse, and recognizes wearer intent including terrain (sloping groundand stairs) context. Here, intent recognition can be accomplishedthrough use of metasensors as follows:

-   -   Kinematic State Estimator (KSR)—The KSR employs a 6-DOF IMU        embedded in the ankle or knee and the knee joint angle, θ₄, to        reconstruct the tibia and femur coordinate systems in        real-time—capturing the inertial path of the ankle, knee and hip        and points between these throughout all or part of a gait cycle.    -   Terrain Modality Discriminator (TMD)—The TMD applies pattern        recognition of the ankle, knee and hip translational and        rotational paths during the swing phase to infer underlying        terrain. The state control processor uses the terrain context to        inform the ankle and knee equilibrium and impedance at foot        strike.    -   Ground Reaction Force/ZMP Estimator (GRFZMP)—The GRFZMP        processes the force-torque sensor data, the ankle joint torque        and the tibia kinematic state to compute the ground reaction        force vector and the zero-moment position of this. This        information may be used by the state control processor in        combination with the KSR. TMD and EIE (below) to determine        locomotion context (walking, sitting, standing, stair climbing)        and/or to apply balance control while standing, walking and        running.    -   External Influence Estimator (EIE)—The EIE may use the GRFZMP        and the KSR information to determine, via inverse dynamic        approximation, the external influences that must be acting on        the trunk (as measured at the hip) to achieve its kinematic        state (of acceleration). The EIE can estimate, for instance, the        presence, and influence of external force as might be applied by        the arms as the bionic leg wearer lifts out of a chair. The EIE        can also estimate the presence and influence of trailing leg        powered plantar flexion on a stair. Such information may be used        by the state control processor to determine when to apply leg        joint torques in such locomotion contexts. Additional details        regarding various embodiments of the leg architecture are        provided in the references incorporated by reference above.

Control Architecture

Embodiments of the leg system employ a loosely-coupled joint controlarchitecture. Here, the ankle state machine and control behaviors arelargely independent of the knee control state. Ankle state machine andcontrol behaviors are described in greater detail in the referencesincorporated by reference above. In particular, thebiophysically-motivated ankle state machine and behaviors are describedin detail in U.S. Provisional Patent Application Ser. No. 61/662,104,entitled “Bionic Control System for an Artificial Ankle Joint.”

A schematic of one embodiment of a knee state machine is illustrated inFIG. 13 . As shown in FIG. 13 , the Knee State Machine (KSM) embodiesfour states Early Stance, Late Stance, Swing Flexion and Swing Extensionwith state-dependent control behaviors and state transitions (ST1, ST4,ST6, ST7 and ST8), as further discussed below.

State-Dependent Control Behaviors

FIG. 14 illustrates the kinematic behavior of the knee during a typicalgait cycle where ES refers to Early Stance: LS refers to Late Stance;ESW refers to Early Swing; LSW refers to Late Swing; θ_(k) refers toKnee Angle; HS refers to Foot Strike; and TO refers to Toe-Off.

Early Stance

In Early Stance, the knee applies a lightly-damped spring responsedefined by stiffness, k_(ES), and damping, b_(ES0). For stance flexion,δθ_(k)=θ_(k)−θ_(0es), when less than about 15°, the early stanceimpedance relation may be provided as follows:

Γ_(k) =−k _(ES)(θ−θ

)−b

{dot over (θ)}  Eq (7)

Where

-   -   Γ_(k)=knee joint torque    -   θ_(es)        =fully extended knee angle setpoint, typically 0 deg

For stance flexion that exceeds about 15°, the joint impedance relationcreates a highly damped response:

Γ_(k) =−b

{dot over (θ)}_(k)  Eq (8)

Equations 7 and 8 may be implemented by using closed-loop torquecontrol, using SEA deflection as a measure of joint torque feedback. Inanother embodiment, the knee SEA may employ a series elasticity withstiffness substantially equal to k_(es). In this way, the motor drivetransmission can be locked at θ_(es0), enabling the series elasticelement to compress and extend without motor movement to account for themaximum early stance knee fluxion for typical level-ground gait cycles.

In another embodiment, the motor may be employed as a programmableclutch (dynamic brake/damper) by shorting the motor leads-applying astrong braking function with a time constant typically in the range ofapproximately 800-1500 milliseconds. Details concerning the use ofshorted leads may be found in U.S. patent application Ser. No.13/417,949, entitled “Biomimetic Joint Actuators.” In such anembodiment, the battery power source may be disconnected from the SEA,thereby eliminating battery consumption during knee flexion andextension in level-ground walking.

In some cases, the shorted-leads may be pulse-width modulated, enablingthe damping to be controlled, e.g., to reduce the damping at largeflexion, while at the same time harvesting energy to charge the bionicleg power source (i.e., battery) during, for example, the swing phase ofwalking. Since the knee joint generally draws net energy, such anembodiment can be used to operate the knee joint at extremely low powerin at least early stance flexion/extension early swing and late swing,even when the battery is disconnected. The shorted leads functionalitycan make possible assertion of a safe state during fault or powerinterruption, thereby protecting the wearer. In some embodiments,k_(es), and b_(es), are functions of time (e.g., may exhibit atime-dependent decay behavior). For instance, the change from astiffness-dominated response to the damping-dominated response may notbe accomplished by crossing an angle threshold, but rather by applying aprogrammable, exponential decay of the stiffness and damping as shown inFIG. 15 , which illustrates an early stance exponential stiffness anddamping response for an embodiment of a knee device.

The stiffness and damping impedance coefficients may be defined by thefollowing relations:

=τ_(k) ² {umlaut over (k)} _(es)(i)+2τ_(k) {dot over (k)} _(es)(t)+1=k_(es) _(min)   Eq (9)

Where

-   -   k_(es)(0)=k_(es) _(min) and    -   τ_(k) is the time constant of the stiffness decay

τ_(b) ² b _(es)(t)+2τ_(b) {dot over (b)} _(es)(t)+1=b _(es) _(max)   Eq(10)

Where

-   -   b_(es)(0)=b_(es) _(max) and    -   τ_(b) is the time constant of the damping decay

As shown in FIG. 15 , the time constant for stiffness decay may be setto be shorter than the damping time constant. Though, in someembodiments, the time constant for stiffness decay may be greater thanthe damping time constant.

In some embodiments, a first-order or higher order differential equationmay be used in place of Eqs. 9 and 10. A second-order response may beadvantageous in that the attenuation is substantively delayed theinitial values are substantially maintained, for a certain amount oftime controlled by the time constant prior to dropping off. Throughthese time varying impedances, the knee will behave during early stanceas an efficient spring during level ground walking, a damper with arelatively high damping value for stair and slope descent, and a lightlydamped knee while sitting.

Late Stance

The joint torque sign reversal at substantially full knee extensionsignals the transition from Early Stance to Late Stance in a typicalgait cycle. In one embodiment, the Late Stance reflex behavior followsthe relation below:

$\begin{matrix}\text{?} & {{Eq}(11)}\end{matrix}$ ?indicates text missing or illegible when filed

Where

-   -   τ_(motor) _(knee) is the SEA motor torque,    -   Γ₀        is a normalizing torque defined by body weight and activity        level, and    -   pff( ) and N( ) are functions of knee torque rate of change at        entry to late stance.

In other embodiments, a neuromuscular model, also employing positiveforce feedback on a modeled Gastrocnemius muscle, may be used. Forfurther details regarding this neuromuscular model, the disclosure ofU.S. Provisional Patent Application Ser. No. 61/595,453, entitled“Powered Ankle Device” may be relevant.

In certain cases—including stair ascent, steep dump ascent and duringthe transition from sitting to standing—the knee joint may be flexedpast a threshold of θ_(k)

, and extending at a substantial rate (|{dot over (θ)}_(k)|>{dot over(ξ)}

) where {dot over (ξ)}

is the rate threshold. In this case, a rate dependent spring stiffness,k_(ex), that applies positive feedback in response to angular rateincreases for an embodiment of a knee device as shown in FIG. 16 a andcaptured in the anti-slip impedance control behavior defined by Eq. 12may be applied.

Γ_(k) =−k

({dot over (θ)} _(k))θ _(k) −b

({dot over (θ)}){dot over (θ)}_(k)  Eq (12)

Where

-   -   b        ({dot over (θ)}) applies light damping to achieve stability when        {dot over (θ)}<0,    -   b        ({dot over (0)}) applies strong damping to resist flexing    -   {dot over (θ)}_(k) is the knee joint angular rate, and    -   θ is the output of a peak detection filter of the form        -   τ_(ext)({dot over (θ)})0+{umlaut over (θ)}={dot over (θ)},            where            -   τ_(ext)({dot over (0)})=τ_(ext)                if {dot over (0)}<0 and            -   τ_(ext)({dot over (θ)})=τ_(ext)                if {dot over (θ)}≥0    -   And where    -   k_(ex)({tilde over ({dot over (θ)})}) of the form shown in FIG.        16 a        In some embodiments, k_(ex) and b_(ex) are time-dependent        functions that exponentially decay over time and are initialized        to the nominal form when retriggered ({dot over (θ)}≥ξ        ). In an “anti-slip” embodiment described here, momentary        flexion velocities do not cause the knee torque to drop—thereby        making it easier for the wearer to maneuver (e.g., to get out of        a chair or to transition to bionic limb support when the sound        side (trailing leg) is pushing off of a stair below the bionic        limb). FIG. 16 s defines the general form of k        illustrating that the flexion stiffness may increase with        increasing joint speed. In some cases, the peak flexion        stiffness may have a lower peak than in extension, enabling the        wearer to more easily flex the knee while sitting. FIGS. 16 b-16        d illustrate schematics of a wearer moving from a sitting        position to a standing upright position.

Swing Flexion

The Early Swing state transition occurs at toe-off, as reported by theankle state machine. In early swing flexion, knee behavior may beballistic for flexion angles less than about 45° (e.g., no spring ordamping) and lightly damped (b=b_(sf)) for greater flexion. Thisbehavior is captured in Eq. 13.

Γ_(k) =−b _(sf){dot over (θ)}_(k)∨θ_(k)<θ_(sf)=0 elsewhere  Eq. (13)

Swing Extension

Once the maximum swing flexion is achieved, the knee state transitionsto swing extension. In early swing extension the behavior is nearlyballistic (e.g., lightly damped) with damping constant, b_(se)=b_(se)

. The damping coefficient increases nearly quadratically as the kneeflexion approaches θ_(k)=θ_(kes)

as shown in three piecewise continuous angle-dependent damping functionembodiments (in swing extension) in FIGS. 17 a-c . FIG. 17 a depicts thebehavior of an embodiment that exhibits piece-wise constant and linearbehavior. FIG. 17 b illustrates the behavior of an embodiment thatexhibits piece-wise linear and quadratic behavior. FIG. 17 c shows thebehavior of another embodiment that exhibits a more general functionalform.

In Swing Extension, such behavior may be captured in Eq. 14.

Γ_(k) =−b _(se)(θ_(k)){dot over (θ)}_(k)  Eq. (14)

Where

-   -   b_(se)(θ_(k)) is defined as a piecewise continuous function per        FIGS. 17 a -c

Damping during Swing Extension may be used to decelerate knee flexion(tibia angular rate) as the joint angle approachesfull-extension—increasing substantially linearly until θ drops below athreshold angle. Below the threshold, the damping increases according toa substantially quadratic function as it approaches θ=0. Such dampingcreates a “sticky” behavior that holds the joint nearfull-extension-preparing the knee to absorb the foot strike energy andto transition to the spring-like behavior in Early Stance.

State Transitions

FIG. 13 illustrates the knee state machine and defines knee controllerstate transitions, as further discussed below.

State Transition 1 (ST1): Swing Extension (or Flexion)-to-Early Stance

The foot strike gait event marks the transition from Swing Extension (orFlexion)-to-Early Stance—a transition that aligns with the Late Swing toEarly Stance transition on the ankle. Here, the world-z component of theground reaction force, as shown in FIG. 18 , will be used to detect theST1 transition (i.e., foot strike transition, heel-strike or toe-downy,defined as:

ST1=(F _(z) >F _(z) _(FS) )  Eq. (15)

Where

-   -   F_(z) _(FS) is the force transition threshold that signals        foot-strike.

In another embodiment as described in U.S. Provisional PatentApplication Ser. No. 61/662,104, entitled “Bionic control System for anArtificial Joints” a logic transition informed by ankle torque andderivatives can be used to accomplish ST1.

State Transition 6 (ST6): Early Stance-to-Late Stance

The Early Stance to Late Stance transition gait event signifies thattoe-loading is occurring when the knee is fully extended as defined bythe logic equation;

$\begin{matrix}\text{?} & {{Eq}.(16)}\end{matrix}$ ?indicates text missing or illegible when filed

Where

-   -   ξ⁺ are ξ⁻ are small angles signifying proximity to full        extension, and    -   Γ_(toe load) is the toe loading threshold as measured at the        ankle, and    -   Γ_(a) signifies the ankle torque reported by the ankle MTU.

In other embodiments, toe loading is detected by determining whether theZMP of a ground reaction force of significant magnitude is substantiallylocated in the forward half of the foot.

State Transition 4 (ST4): Late Stance (or Early Stance)-to-Swing Flexion

The toe-off gait event signals the transition to Swing Flexion fromeither Late Stance or Early Stance. ST4 is defined as:

ST1=(F _(z) <F _(z) _(toe off) )  Eq. (17)

Where

-   -   F_(z) is the z-component of the ground reaction force, and    -   F_(z) _(toe off) is the toe-off force threshold.        In other embodiments, substantially zero torque, as reported by        the ankle MTU, can be used to detect the toe-off condition. In        another embodiment described in U.S. Provisional Patent        Application Ser. No. 61/662,104, entitled “Bionic Control System        for an Artificial Joint,” ankle torque and derivatives        (Γ_(ankle)≈0) can be used as input for triggering or modulating        parameters of the ST4 transition.

State Transition 7 (ST7): Swing Flexion-to-Swing Extension

The state transition from Swing-Flexion to Swing Extension is marked bya sign reversal in the knee angular velocity detected here as the timewhen the knee velocity goes to zero at a time sufficiently aftertoe-off:

$\begin{matrix}\text{?} & {{Eq}.(18)}\end{matrix}$ ?indicates text missing or illegible when filed

Where

-   -   t        is the time elaplsed since toe-off, t        is the minimum duration threshold, and    -   {dot over (ξ)}⁺ and {dot over (ξ)}⁻ define the small velocity        boundary.

State Transition 8 (ST8): Late Stance-to-Early Stance

In some circumstances, e.g. when the wearer is standing quietly and thenenters Late Stance and then flexes the knee, it may be appropriate forthe state machine to transition back to early stance. The logic isdefined as follows:

$\begin{matrix}\text{?} & {{Eq}.(19)}\end{matrix}$ ?indicates text missing or illegible when filed

Where

-   -   θ_(k) _(torque) defines the angle threshold, and    -   ξ_(Γ) ⁻ and ξ_(Γ) ⁺ define the small torque detection        boundaries.

OTHER EMBODIMENTS Self-Adjusting Joint Equilibrium

In this embodiment, the joint equilibrium tracks the joint angle with aprogrammable convergence preferably through use of a first orsecond-order tracking filter with time constant, τ. In some embodiments,the system is configured for the joint equilibrium to exhibittime-dependent behavior that relaxes to an equilibrium that issubstantially equivalent to the current joint angle. That is, inaccordance with the system exhibiting a programmable convergence, thejoint equilibrium of the system continually, yet gradually, tracks thecurrent joint angle. For example, if the joint angle does not changeafter a long period of time, then the joint equilibrium graduallyrelaxes from an initial value to a value equal to that of the currentjoint angle.

In some embodiments, self-adjusting joint equilibrium behavior may begoverned by the following relationships:

Γ=−k(θ−θ₀)−b{dot over (θ)}  Eq. 20

τ₀{dot over (θ)}₀+{dot over (θ)}₀=θ  Eq. 21

Equation 21 is inserted into Eq. 20 and the resulting relationship issubject to a Fourier transform, where the function is transformed fromthe time domain to the frequency domain. Accordingly, the derivativerepresented by ({dot over ( )}) is replaced with s=jω and

? ?indicates text missing or illegible when filed

resulting in an impedance relation of the form:

$\begin{matrix}\text{?} & {{Eq}.22}\end{matrix}$ ?indicates text missing or illegible when filed

where H (s) is defined by the relation.

$\begin{matrix}\text{?} & {{Eq}.23}\end{matrix}$ ?indicates text missing or illegible when filed

FIG. 19 illustrates the impedance transfer function,

? ?indicates text missing or illegible when filed

represented by Eq. 22.

The frequency response of this impedance law has interesting properties.At low frequencies, the impedance behaves as a damper with coefficient,b*=b+kτ. At medium frequencies, the impedance has stiffness propertieswith an equivalent stiffness of

? ?indicates text missing or illegible when filed

And at high frequencies, the impedance behaves as a damper withequivalent damping of

? ?indicates text missing or illegible when filed

is the transition frequency between the first damping and stiffnessbehaviors. Here, ω₀ may range from 0-13 rad/sec (0-2 Hz) providing aprimarily damping response in that range. Between ω_(theta) and about 60rad/sec (a preferred range between 5-20 Hz), a stiffness dominatedresponse is applied. Above this latter frequency defined by

? ?indicates text missing or illegible when filed

a damping-dominated response is applied. Often wearers complain that itis hard to maintain balance when the leg joints are in a substantiallylightly damped state. So by implementing this method, improved stabilityresults because in the frequency range between 1-10 Hz astiffness-dominated response is applied that serves to restore balance.

Blended Reflex,

The following disclosure describes two blended reflex methods, eachblending (interpolating) independently tuned responses—defined by torquegain (P_(ff)) and torque exponent (N), at a fast and a slow walk speed.At speeds below the “slow-walk” speed as determined by the wearer (e.g.,less than 0.75 m/s), the reflex employs a slow-walk parameter set; atspeeds greater than the fast-walk speed as determined by the wearer(e.g., greater than 1.75 m/s), the reflex employs the fast walkparameter set; and at speeds in between, the reflex adds the tworesponses together in accordance with a linear or non-linearinterpolation based upon walking speed, a surrogate for walking speed(e.g., pitch rate in mid-stance), a kinetic (e.g., torque rate) orkinematic (e.g., joint angle rate). The term walking speed and operatingspeed below may loosely refer to the walking speed, surrogates ofwalking speed, a suitable kinetic rate or a suitable kinematic rate.

Other interpolations may be used, and more than two speed-registeredresponses may be blended through more complex interpolation, forexample, based upon the “distance” between the operating speed and eachof the tuned speeds. This approach may be advantageous over the existingmethods in that both the gain and exponent can be independentlycontrolled—that is, these reflex coefficients can be tuned independentlyof each other. For instance, a slow walk reflex response may require alower exponent torque than that required by a fast walk reflex response,and vice-versa. With fixed N (the variable that controls timing), thereis a tradeoff between slow-walk consistency and fast walk power andbattery economy. By applying independent tuning, an optimum performancemay be achieved, at both ends of the walking speed spectrum, and overallwearer experience can be improved.

Method I blends two torque models—one defined at a slow speed and one atthe fast speed, as determined by the wearer—with gain, P_(ff)({dot over(s)}_(slow)), and exponent, N({dot over (s)}_(slow)), for a first(“slow-walk”) torque model; and gain, P_(ff)({dot over (s)}_(fast)), andexponent, N({dot over (s)}_(fast)), for a second (“fast-walk”) torquemodel. Method II blends the gains and exponents into a single torquemodel—with gain, P({dot over (s)}), and exponent, N({dot over (s)}),where the gain and exponent are speed interpolated (via linear ornon-linear interpolation) across the speed domain, [{dot over(s)}_(slow), {dot over (s)}_(fast)]. The blended torque models areexpressed by suitable computations below.

Method I: Blended Torque Models

? ? ? ? ? ? ? ?indicates text missing or illegible when filed

Method II: Blended Coefficients

? ?indicates text missing or illegible when filed

Where

-   -   P _(ff)({dot over (s)})=c₁({dot over (s)})P_(ff)({dot over        (s)}_(slow)+c₂P_(ff)({dot over (s)}_(fast))    -   and    -   N({dot over (s)})=c₁({dot over (s)})N({dot over        (s)}_(slow))+c₂N({dot over (s)}_(fast))        Where c₁ and c₂ are defined as in Method I.

Non-Linear Distance-Based (Quadratic Non-Linear Interpolation)

? ? ? ? ?indicates text missing or illegible when filed

FIGS. 20-23 illustrate ankle data gathered from test subjects of walkinginformation that are used as design parameters for the control ofartificial leg devices in accordance with the present disclosure.Accordingly, embodiments provided herein may employ this data to createa dashboard of normative measures across walking speed that capture thekinetics and kinematics of natural limbs. In some embodiments of thecontrol architecture described above, the kinetic and kinematic responseof the bionic ankle joint is projected onto this dashboard of normativemeasures. The impedance, equilibrium and torque, including reflex,modulation may then be optimized to fit within the normative statisticalrange noted in the dashboard. Bionic restoration of ankle-foot function,as measured by the closeness of fit, is thereby achieved. And thisprojection of kinetic and kinematic measures onto the dashboard servesas a record that can be used by the clinician to prove the efficacy ofthe bionic limb as this might be needed for insurance reimbursement orother purposes.

FIG. 20 shows graphs that depict ankle angle, angular velocity, moment,and power plotted as a percentage of the gait cycle. Plots are shown forthe average of all subjects walking at their fast walking speed (e.g.,between 1.5-2.5 m/s). As further shown, the stance phase is divided intothree subphases—controlled plantar flexion (CP), controlled dorsiflexion(CD) and powered plantarflexion (PP). Various embodiments of the presentdisclosure may employ principles described in the Masters Thesis byGates, D. H, entitled “Characterizing Ankle Function During StairAscent, Descent, and Level Walking for Ankle Prosthesis and OrthosisDesign.” submitted in 2004, the disclosure of which is herebyincorporated herein by reference in its entirety.

FIG. 21 depicts a scatter plot graph of the net non-conservative anklework (W_(NET)=W_(PP)−(W_(CP)+W_(CD))) on level-ground performed bywalkers with an intact ankle (population N=70) during the stance phaseof gait as a function of walking speed. Each point represents theaverage work done for all trials of a subject when asked to walk at acertain speed (fast, normal, slow). A linear regression was performed onthe mean work for each subject walking at his or her mean speed. Thisline shows a significant increase in ankle work, and linear correlationwith gait speed. The rate-dependent, blended reflex disclosed above maybe optimized to achieve a close fit to this linear net non-conservativeankle work vs. walking speed relationship.

FIG. 22 illustrates the correlation between ankle torque and each ofankle angle and ankle velocity, during a single gait cycle. Data areShown for an average of all subjects walking at fast, normal, and slowspeeds. Trials were normalized to 50 equally spaced data points, whichwas then averaged for each subject. Numbers mark the beginnings and endsof subphases of gait (CP: 1-2, CD: 2-3, PP: 3-4). As shown, at normalwalking speeds, the ankle torque correlates strongly with ankle positionduring these subphases. As further shown, the faster the walking speed,the greater the net amount of work performed by the ankle (shown by thearea under the curve for the ankle angle versus ankle torque graphs).

FIG. 23 shows graphs of ankle torque versus ankle angle plotted for eachsubphase of stance for walking subjects. Data are shown for the averageof all subjects walking at their self-selected slow, normal and fastspeeds. For the CP phase (top), there is a generally linear relationshipat each walking speed. For the CD phase (middle), the relationshipincreases in non-linearity as speed increases. For the final phase, PP,the fitting is generally linear.

It should also be understood that, unless clearly indicated to thecontrary, in, any methods claimed herein that include more than one stepor act, the order of the steps or acts of the method is not necessarilylimited to the order in which the steps or acts of the method arerecited.

While aspects of the invention have been described with reference tovarious illustrative embodiments, such aspects are not limited to theembodiments described. Thus, it is evident that many alternatives,modifications, and variations of the embodiments described will beapparent to those skilled in the art. Accordingly, embodiments as setforth herein are intended to be illustrative, not limiting. Variouschanges may be made without departing from the spirit of aspects of theinvention.

What is claimed is:
 1. A prosthesis, orthosis or exoskeleton device,comprising: a joint constructed and arranged to permit flexion andextension between a proximal member and a distal member; a motorizedactuator configured to apply at least one of a joint impedancereferenced to a joint equilibrium or a joint torque; a sensor configuredto detect a characteristic of the device; and a controller configured tomodulate a parameter comprising at least one of the joint equilibrium,the joint impedance and the joint torque according to the detectedcharacteristic, the modulated parameter exhibiting time-dependent decaybehavior.
 2. The device of claim 1, wherein the detected characteristiccomprises at least one of a phase and a change in a phase of jointmotion in a repetitive cycle, each occurrence of the cycle comprising aplurality of phases; and the time-dependent decay behavior comprises adecaying time response to the modulated parameter according to at leastone of the detected phase and the detected change in phase of jointmotion, wherein a duration of the time-dependent decay behaviorcomprises at least one phase of the one cycle.
 3. The device of claim 1,wherein the joint torque comprises a positive force-feedback componentcomprising at least one of a gain and an exponent as applied to thejoint torque.
 4. The apparatus of claim 3, wherein the at least one ofthe gain or the exponent are modulated as a function of at least one ofa proximal member angular rate, a distal member angular rate and atorque rate.
 5. The device of claim 4, wherein the positive forcefeedback component comprises a function of a rate of change of at leastone of a joint torque and an actuator torque.
 6. The device of claim 1,wherein the modulated parameter comprises at least one of a proximalmember angular rate, a distal member angular rate and at least one of ajoint torque rate and an actuator torque rate.
 7. The device of claim 1,wherein the time-dependent decay behavior comprises an exponentialdecay.
 8. The device of claim 1, wherein the sensor is configured todetect a joint position and the controller is configured to modulate thejoint equilibrium to converge with the detected joint position.
 9. Theapparatus of claim 1, wherein the device is a knee prosthesis, orthosisor exoskeleton.
 10. The device of claim 1, wherein the joint impedanceincludes at least one of a stiffness and damping.
 11. The device ofclaim 10, wherein the stiffness comprises an early stance flexionstiffness.
 12. The apparatus of claim 10, wherein the stiffnesscomprises a knee flexion stiffness that is a function of knee jointangular rate.
 13. The apparatus of claim 1, wherein the joint torque isin a late stance and is a positive force feedback component.
 14. Theapparatus of claim 13, wherein the positive force feedback componentmodulates a positive force feedback as a function of a rate of change ofthe joint torque.
 15. The apparatus of claim 14, wherein the at leastone of the gain or the exponent are modulated according to at least oneof the detected phase and a change in the detected phase.
 16. A methodcomprising: actuating the motorized actuator of claim 1 to apply the atleast one of the joint impedance or the joint torque; and applying thecontroller to modulate the parameter.
 17. The method of claim 16,wherein the detected characteristic comprises at least one of a phaseand a change in a phase of joint motion in a repetitive cycle, eachoccurrence of the cycle comprising a plurality of phases; and thetime-dependent decay behavior comprises a decaying time response to themodulated parameter according to at least one of the detected phase andthe detected change in phase of joint motion, wherein a duration of thetime-dependent decay behavior comprises at least one phase of the onecycle.
 18. The method of claim 16, wherein the joint torque comprises apositive force-feedback component comprising at least one of a gain andan exponent as applied to the joint torque.
 19. A controller for aprosthesis, orthosis or exoskeleton device comprising a jointconstructed and arranged to permit flexion and extension between aproximal member and a distal member, a motorized actuator configured toapply at least one of a joint impedance referenced to a jointequilibrium or a joint torque, and a sensor configured to detect acharacteristic of the device, the controller comprising a processor; anda non-transitory computer-readable medium storing instructions that,when executed by the processor, configure the processor to: modulate aparameter comprising at least one of the joint equilibrium, the jointimpedance and the joint torque according to the detected characteristic,the modulated parameter exhibiting time-dependent decay behavior. 20.The controller of claim 19, wherein the detected characteristiccomprises at least one of a phase and a change in a phase of jointmotion in a repetitive cycle, each occurrence of the cycle comprising aplurality of phases; and the time-dependent decay behavior comprises adecaying time response to the modulated parameter according to at leastone of the detected phase and the detected change in phase of jointmotion, wherein a duration of the time-dependent decay behaviorcomprises at least one phase of the one cycle.